Electrochemical detection of peroxide-containing compounds

ABSTRACT

A sensing electrode, and an electrochemical system and method utilizing same for detecting peroxide-containing compounds in a sample, are provided. The sensing electrode is a carbon electrode having ions of a metal that promotes decomposition of a peroxide absorbed to its surface, optionally along with a solid electrolyte membrane.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/008,215 filed on Jun. 14, 2018, which claims the benefit of priorityunder 35 USC § 119(e) of U.S. Provisional Patent Application No.62/519,977, filed on Jun. 15, 2017.

The contents of the above applications are all incorporated by referenceas if fully set forth herein in their entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to detectionof chemicals and, more particularly, but not exclusively, to electrodes,and to systems and methods employing same, usable in electrochemicaldetection of peroxide-based compounds such as peroxide-based explosives.

An ‘explosive’ is a chemically-unstable molecule having a rapid rate ofautodecomposition, with the accompanying evolution of large amounts ofheat and gaseous products. There has been a great increase in thedevelopment of trace and ultra-trace explosive detection in the lastdecade, mainly due to the globalization of terrorist acts, and thereclamation of contaminated land previously used for military purposes.

In addition, the availability of raw materials for the preparation ofexplosives, together with the growing access to information on preparingthese explosives, allows for almost anyone with sufficient will andinternet access to prepare a bomb. The vast number of people passingthrough borders, public places, airports etc. poses a huge challenge forcurrent day security screening technologies. The same challenge appliesto homes and buildings security. The ultimate goal is to be able torapidly and effectively screen every passing person, without the need todelay the traffic of people, and without human contact if possible.

Explosives, especially concealed ones, have a very low vapor pressure or‘signature’ in the surrounding air. The effective vapor pressure ofexplosives can be reduced by a factor of up to 1000, with the use ofplastic packages. Detection methods for traces of explosives thereforecontinue to be plagued by the low volatility of many target analytes.

One of the most commonly-used high explosives over the last 100 years is2,4,6-trinitrotoluene (TNT), which poses not only a direct securitythreat, but also great environmental concern due to soil and watercontamination near production, storage and test sites. Other nitro-basedexplosives are also in use.

Peroxides-based explosives (e.g., cyclic organic peroxides) have alsobeen used recently to build improvised explosive devices, increasingworldwide the awareness thereto. Development of methodologies for thedetection of triacetone triperoxide (TATP), hexamethylene triperoxidediamine (HMTD), tetramethylene diperoxide dicarbamide (TMDD) and othercyclic organic peroxides have become an urgent priority. Most organicperoxides are explosive, and some compounds can be easily synthesized bymixing common commercial products such as acetone, hydrogen peroxide andstrong acids. Most of the current technology in use for trace detectionof explosives is unable to detect peroxide-based explosives [Oxley etal. Propellants, Explosives, Pyrotechnics 34, 539-543 (2009); Önnerud,H., Wallin, S. & Östmark, H. in Intelligence and Security InformaticsConference (EISIC), 2011 European. 238-243 (IEEE)].

Past theoretical studies have showed a plausible approach based on theformation of complexes between the molecular ring structures of cyclicorganic peroxide explosives and a central metal moiety, analogous to theformation of clatherates and crown ethers that selectively bind to ionicspecies in solution. These studies have predicted that TATP moleculescan bind to several ions of different valency, with In³⁺, Zn²⁺ and Ti⁴⁺showing the highest binding energy [Dubnikova, F., Kosloff, R., Zeiri,Y. & Karpas, Z. The Journal of Physical Chemistry A 106, 4951-4956(2002)].

Analytical procedures in use today for the trace detection of explosivestypically involve collecting vapor samples and analyzing them with asensitive method. Several methodologies have been reported for detectingTNT and other nitro-based explosives. These are based onelectrochemistry, ion-mobility spectrometry, gas chromatography,high-performance liquid chromatography, surface enhanced Ramanspectroscopy, nuclear quadrupole resonance, neutron activation analysis,photoluminescence, surface acoustic-wave devices, microcantilevers,fluorescent polymers, surface plasmon resonance, quartz crystalmicrobalance, immunosensors and other methods. These methods arereliable for explosives detection, but involve time-consumingprocedures, high costs and operation by well qualified staff, whichlimits their application in field conditions.

Additional methods involve trained animals including dogs, mice and beesand utilize their highly sensitive sense of smell for traces explosivedetection. These methods however require intense and expensive trainingof the animal, and handling by an expert.

While a large number of techniques are reported for the detection ofnitro based explosives such as TNT, detection of peroxide-basedexplosives is more complicated.

For example, while several detection methodologies rely on thechromophoric nitro groups present in TNT, peroxide-based explosivetypically lack chromophoric groups.

Several direct methods for detection of peroxide-based explosives havebeen reported, including, for example, mass spectrometry, liquidchromatography-mass spectrometry, gas chromatography-mass spectrometry,Ion-mobility spectrometry-mass spectrometry and high-performance liquidchromatography. See, for example, Cotte-Rodriguez et al. ChemicalCommunications, 953-955, doi:10.1039/b515122h (2006); Widmer et al.Analyst 127, 1627-1632, doi: 10.1039/b208350g (2002); Sigman et al.Rapid Communications in Mass Spectrometry 20, 2851-2857, doi:10.1002/rcm.2678 (2006); Buttigieg et al. Forensic Science International135, 53-59 (2003); and Schulte-Ladbeck, R. & Karst, U. Analytica ChimicaActa 482, 183-188 (2003).

However, these methods suffer from relatively high costs, extensiveoperator skills, and limited field portability.

A few methods for a rapid detection of peroxide-based explosives basedon decomposition of these compounds to hydrogen peroxide in the presenceof an acid or ultraviolet radiation and its detection by photometricaland electrochemical methods have also been suggested. See, for example,Schulte-Ladbeck, et al. Analytical Chemistry 75, 731-735, doi:Doi10.1021/Ac020392n (2003); Schulte-Ladbeck, R. & Karst, U. AnalyticaChimica Acta 482, 183-188 (2003); Schulte-Ladbeck et al. Analyst 127,1152-1154, doi:Doi 10.1039/B206673b (2002); Munoz et al. Analyst 132,560-565, doi:Doi 10.1039/B701356f (2007); Lu et al. Analyst 131,1279-1281, doi:Doi 10.1039/B613092e (2006); and Eren, S. et al. Analyst135, 2085-2091, doi:Doi 10.1039/B925653a (2010).

Electrochemical detection methods utilize electrodes, immersed in anelectrolyte, and connected to a potentiometer, which measure the currentthat flows between the electrodes upon potential application. Typically,during an electrochemical reaction the electrode potential is varied;and an electric current flows between the electrodes that ischaracteristic of the presence of an electrochemically reactivesubstance in the electrolyte. Electrochemical detection typically meetsmost of the above requirements of a robust and efficient methodology fordetection of explosives. See, Caygill, J. S., Davis, F. & Higson, S. P.J. Current trends in explosive detection techniques. Talanta 88, 14-29,doi:DOI 10.1016/j.talanta.2011.11.043 (2012); Wang, J. Electrochemicalsensing of explosives. Electroanal 19, 415-423, doi:DOI10.1002/elan.200603748 (2007).

Most electrochemical methods for peroxide-based explosives detectionrely on the detection of H₂O₂ formed from the acid or ultravioletdecomposition of the explosive material. Prussian-blue andFe^(II)/^(III) ethylenediaminetetraacetate are examples of chemicalmodifications on a working electrode that are used in those methods.Additional examples include electrochemical detection of TATP performedby redox reaction with bromide ion at 55° C. Acetone and bromine,obtained in such a reaction, interact to give acetone bromides, suchthat a lack of free bromine is indicative of the presence of theexplosive. Another example is the detection of HMTD usingelectro-generated chemiluminescence (ECL), while utilizing the tertiaryamine moieties present in HMTD. See, for example, Schulte-Ladbeck et al.Analyst 127, 1152-1154, doi:Doi 10.1039/B206673b (2002); Lu et al.Analyst 131, 1279-1281, doi:Doi 10.1039/B613092e (2006); Laine et al.Analytica Chimica Acta 608, 56-60, doi:DOI 10.1016/j.aca.2007.12.003(2008); Laine et al. Microchem J 91, 78-81, doi:DOI10.1016/j.microc.2008.08.005 (2009); Zhao et al. Journal ofElectroanalytical Chemistry 379, 501-503, doi:Doi10.1016/0022-0728(94)87175-2 (1994); Xie, Y. Q. & Cheng, I. F.,Microchem J 94, 166-170, doi:DOI 10.1016/j.microc.2009.10.016 (2010);Parajuli, S. & Miao, W. J., Analytical Chemistry 81, 5267-5272, doi:Doi10.1021/Ac900489a (2009).

One of the most pronounced limitations in electrochemical measurementunder atmospheric conditions is the presence of dissolved oxygen in asample. The dissolved oxygen concentration in aqueous electrochemicalsolution is about 0.25 mM (about 8 ppm) [Julia, P. L. C. & Coso, E. B.Homenatge professor Josep M.Costa (eBooK) 2a part. Trends inelectrochemistry and corrosion at the beginning of the 21st century.(Publicacions i Edicions de la Universitat de Barcelona, 2004)] and ismuch higher in non-aqueous electrochemical solutions [Achord, J. M. &Hussey, Analytical Chemistry 52, 601-602, (1980)]. The oxygen is reducedpractically at the same potentials as peroxides-based explosives, and,since oxygen concentration is higher by several orders of magnitude thanthat of the explosive traces, signals generated by the peroxide-basedexplosives traces are substantially masked. This limitation is typicallytreated by deaeration; the oxygen is removed by means of bubbling inertgas, for example argon or nitrogen. Typically, 10-15 minutes ofdeaeration are required in order to obtain efficient oxygen removal in asample of approximately 5 ml. This lengthy procedure is not in line withthe requirements for real time detection of nitro-containing explosives[W. Chen, Y. Wang, C. Bruckner, C. M. Li, Y. Lei, Sensor Actuat B-Chem2010, 147. 191-197].

In addition, a major overlap of the reduction peak of traces of H₂O₂,which may be found in field conditions, and that of a peroxide-basedexplosive further complicate the electrochemical detection, oftenleading to “false positive” detection. See, for example, Butler et al.Talanta 41, 211-215, (1994); Marinovic et al. Journal ofElectroanalytical Chemistry 648, 1-7, (2010).

WO 2011/154939 describes nanodevices which utilize functionalizednanowires for detecting nitro-containing compounds. The nanowiresfeature a functional moiety that interacts with a nitro-containingcompound by forming a charge-transfer complex therewith.

WO 2005/050157, WO 2006/090401, and WO 2007/029245 teach systems fordetecting traces of nitro-aromatic compounds in air, which utilizecarbon electrodes modified by amino-aromatic compound ornitrogen-containing heterocyclic compounds.

WO 2014/111944 describes nanodevices which utilize functionalizednanowires for detecting peroxide-based and/or nitro-containingexplosives.

Additional background art includes Spalek ET AL. J Chem Soc Farad T 178, 2349-2359, doi:Doi 10.1039/F19827802349 (1982); Weiss, J.Transactions of the Faraday Society 31, 1547-1557 (1935); Sheppard, S.A. et al. Analyst 123, 1923-1929, doi:Doi 10.1039/A803310b (1998); andChaki et al. Chemical Communications, 76-77, doi:Doi 10.1039/B107965b(2002).

Yet additional background art includes Chaubey, A. & Malhotra, B. D.Mediated biosensors. Biosens Bioelectron 17, 441-456, (2002); Zang etal. Analytica Chimica Acta 683, 187-191, (2011); U.S. Pat. No.6,872,786; Chen et al. Sensor Actuat B-Chem 147, 191-197, (2010);Filanovsky, B. et al. Adv Funct Mater 17, 1487-1492, (2007);Grigoriants, I. et al. Electrochim Acta 54, 690-697, (2008); Guo et al.Electroanal 23, 885-893, (2011); Chen et al. Chemistry—An Asian Journal6, 1210-1216, (2011); Wang et al. Sensors-Basel 11, 7763-7772, (2011);Cizek, K. et al. Analytica Chimica Acta 661, 117-121, (2010); Galik etal. Electroanal 23, 1193-1204, doi:DOI 10.1002/elan.201000754 (2011); WO2010/112546; WO 2010/227382; WO 2015/059704; WO 2017/098518; Engel, Y.et al. Angew Chem Int Edit 49, 6830-6835, (2010); Dwivedy et al. Journalof Chromatography A 29, 120-125 (1967); and Lichtenstein, A. et al. NatCommun 5, (2014).

SUMMARY OF THE INVENTION

The present inventors have now designed and successfully practiced anovel sensing system for electrochemical detection ofperoxide-containing compounds. The designed system can performelectrochemical detection of trace amounts of peroxide-containingexplosives efficiently in the presence of one or both hydrogen peroxideand dissolved oxygen in a single measurement. The sensing system can beoperated such that detectable concentration of a peroxide-containingcompound is lower than 500 ppb and even lower, and at a detection timeof less than 20 seconds, and is therefore highly useful in fieldconditions.

The sensing system disclosed herein is based on a carbon electrode,preferably a carbon fiber electrode, more preferably, a carbon fibermicroelectrode, modified at its surface by absorbing thereto ions of ametal that promotes peroxide decomposition, optionally together with anion-permeable material.

The sensing system and methods disclosed herein meet the requirements ofa sensitive and robust methodology for detection of explosives by beinghighly sensitive, selective (sophisticated) and working in real timeregime, while at the same time, it features a high sampling rate andmultiplex capabilities, while maintaining handling simplicity andreliability. The sensing system disclosed herein can be designed as handheld devices, with minimized and miniaturized dimensions, weight andcosts.

According to an aspect of some embodiments of the present inventionthere is provided a sensing electrode comprising a carbon electrode anda functional moiety being in association with (e.g., attached orabsorbed to) at least a portion of a surface of the electrode. Accordingto some of any of the embodiments described herein, the functionalmoiety promotes decomposition of hydrogen peroxide.

According to an aspect of some embodiments of the present inventionthere is provided a sensing electrode comprising a carbon electrode anda plurality of functional moieties being in association with (e.g.,attached to absorbed to) at least a portion of a surface of theelectrode. According to some of any of the embodiments described herein,the functional moiety promotes decomposition of hydrogen peroxide.

According to some of any of the embodiments of the present inventionthere is provided a sensing electrode comprising a carbon electrode anda functional moiety being is association with (e.g., attached orabsorbed to) at least a portion of a surface of the electrode, thefunctional moiety comprising at least one metal species that promotesdecomposition of hydrogen peroxide.

According to some of any of the embodiments described herein, thefunctional moiety is absorbed to at least a portion of the surface ofthe electrode.

According to some of any of the embodiments described herein, the carbonelectrode is a carbon fiber electrode.

According to some of any of the embodiments described herein, theelectrode is a carbon fiber microelectrode.

According to some of any of the embodiments described herein, theelectrode is a carbon paper microelectrode.

According to some of any of the embodiments described herein, the carbonelectrode is a gas-permeable carbon electrode, for example, a gaspermeable carbon paper microelectrode or a gas-permeable carbon fabricelectrode, or a gas permeable carbon fiber electrode.

According to some of any of the embodiments described herein, the metalspecies is selected from elemental metal, a metal oxide, a metal ion,and an organometallic complex of any of the foregoing.

According to some of any of the embodiments described herein, the metalspecies is selected from elemental metal, a metal oxide and a metal ion.

According to some of any of the embodiments described herein, thefunctional moiety comprises metal ions.

According to some of any of the embodiments described herein, the metalions undergo reduction to thereby provide metal particles, uponapplication of a potential in a range of from about −0.05 to about 2volts.

According to some of any of the embodiments described herein, thefunctional moiety further comprises particles of the metal (e.g., ofelemental metal).

According to some of any of the embodiments described herein, an amountof the particles of the metal is less than 70 mol %, or less than 65 mol%, of the total number of moles of the metal in the functional moiety.

According to some of any of the embodiments described herein, a molratio of the metal ions and the particles of the metal ranges from 70:30to 30:70.

According to some of any of the embodiments described herein, the metalis selected from silver, rhodium, palladium, iridium, gold, platinum,iron, copper, hafnium, manganese, iridium, gadolinium, cerium, lead, andbismuth.

According to some of any of the embodiments described herein, the metalis silver.

According to some of any of the embodiments described herein, thefunctional moiety comprises at least one metal species having an organicmoiety associated therewith.

According to some of any of the embodiments described herein, at leastone metal species having an organic moiety associated therewith isselected from an organic salt of the metal, and an organometalliccomplex of the metal and an organometallic complex of an oxide of themetal.

According to some of any of the embodiments described herein, at leastone metal species having an organic moiety associated therewith is anorganic salt of the metal, comprising a metal ion and an organic anion.

According to some of any of the embodiments described herein, the metalis silver and the organic salt of the metal is silver benzoate.

According to some of any of the embodiments described herein, theelectrode further comprises an ion-permeable material absorbed to thesurface.

According to some of any of the embodiments described herein, theion-permeable material comprises a polymeric film.

According to some of any of the embodiments described herein, theion-permeable material is or comprises Nafion®.

According to some of any of the embodiments described herein, thefunctional moiety physically interacts with the ion-permeable material.

According to some of any of the embodiments described herein, theelectrode comprises an organic salt of the metal and the polymeric filmabsorbed to the surface.

According to some of any of the embodiments described herein, theelectrode is usable for determining a presence and/or level of aperoxide-containing compound in a sample.

According to an aspect of some embodiments of the present inventionthere is provided a sensing system comprising a sensing electrodeaccording to any of the respective embodiments and any combinationthereof, the sensing electrode being connectable to a power source.

According to some of any of the embodiments described herein, thesensing electrode forms a part of an electrochemical cell.

According to some of any of the embodiments described herein, theelectrochemical cell further comprises a reference electrode.

According to some of any of the embodiments described herein, theelectrochemical cell further comprises an auxiliary electrode.

According to some of any of the embodiments described herein, the systemis operable upon contacting the sensing electrode with an electrolyte.

According to some of any of the embodiments described herein, theelectrochemical cell further comprises an inlet port or any other meansfor introducing the electrolyte solution.

According to some of any of the embodiments described herein, theelectrochemical cell further comprises an electrolyte, and wherein atleast a portion of the sensing electrode contacts the electrolyte.

According to some of any of the embodiments described herein, theelectrolyte features an alkaline pH.

According to some of any of the embodiments described herein, theelectrolyte comprises a mixture of an aqueous solvent and an organicsolvent.

According to some of any of the embodiments described herein, theelectrolyte comprises a quaternary ammonium salt.

According to some of any of the embodiments described herein, the systemfurther comprises a sample inlet or any other means for contacting thesample with the sensing electrode.

According to some of any of the embodiments described herein, the systemfurther comprises a sample inlet or any other means for introducing asample to the electrochemical cell.

According to some of any of the embodiments described herein, the systemfurther comprises a gas outlet.

According to some of any of the embodiments described herein, the systemis devoid of means for deaerating the electrochemical cell prior tocontacting the system with a sample.

According to some of any of the embodiments described herein, theelectrochemical cell further comprises a power source electricallyconnected to the sensing electrode.

According to some of any of the embodiments described herein, the systemfurther comprises a device for measuring an electrochemical parameter ofthe sensing electrode.

According to some of any of the embodiments described herein, the systemfurther comprises an electrical current measuring device for measuringan electrical current or a change in an electrical current generated atthe sensing electrode.

According to some of any of the embodiments described herein, the powersource is configured to apply a varying potential to the sensingelectrode.

According to some of any of the embodiments described herein, the systemfurther comprises a device for determining a change in the electricalcurrent in response to the varying potential.

According to some of any of the embodiments described herein, the systemis configured such that upon application of a potential, a portion ofthe metal species is in a form of metal particles, the portion being nomore than 70 mol % of the total amount of the metal species.

According to some of any of the embodiments described herein, thefunctional moiety comprises metal ions and wherein upon application of apotential, a portion of the metal ions is converted into the metalparticles, the portion being no more than 50 mol % of the amount of themetal ions.

According to some of any of the embodiments described herein, thefunctional moiety comprises particles of a metal and ions of the metal,the system being configured such that upon application of a potential, amol ratio of the ions of the metal and the particles of the metal rangesfrom 75:25 to 25:75.

According to some of any of the embodiments described herein, theelectrochemical cell is configured such that upon contacting a samplecontaining a peroxide-containing compound with the sensing electrode, apresence and/or level of an electrochemical parameter generated inresponse to applying potential to the sensing electrode is indicative ofa presence and/or level of the peroxide-containing compound.

According to some of any of the embodiments described herein, the systemis configured for determining a change in the electrical current inresponse to a varying potential applied to the sensing electrode, thechange being indicative of a presence and/or level of theperoxide-containing compound.

According to some of any of the embodiments described herein, the systemfurther comprises a data processor configured to determine a level ofthe peroxide-containing compound in a sample, the determining beingusing at least one of (i) a calibration curve stored on a computerreadable medium, (ii) a lookup table stored on a computer readablemedium, and (iii) a predetermined relationship between a currentgenerated by the peroxide-containing compound and the level.

According to some of any of the embodiments described herein, thepredetermined relationship comprises a linear relationship.

According to an aspect of some embodiments of the present inventionthere is provided a method of detecting a peroxide-containing compoundin a sample, the method comprising:

contacting the sample with a sensing electrode according to any of therespective embodiments and any combination thereof;

applying a potential to the sensing electrode; and

measuring an electrochemical parameter of the sensing electrode, whereina presence and/or level of the parameter is indicative of a presenceand/or level of the peroxide-containing compound in the sample.

According to some of any of the embodiments described herein, contactingthe sensing electrode with the sample comprises introducing the sampleto a sensing system according to any of the present embodiments (e.g.,by means of an air pump).

According to some of any of the embodiments described herein, theelectrochemical parameter comprises an electrical current generated atthe sensing electrode, wherein a presence and/or level of the electricalcurrent is indicative of a presence and/or level of theperoxide-containing compound.

According to some of any of the embodiments described herein, contactingthe sample with the sensing electrode comprises contacting anelectrolyte solution comprising the sample with the sensing electrode.

According to some of any of the embodiments described herein, the methodis devoid of deaerating the system.

According to some of any of the embodiments described herein, the sampleis a fluid sample.

According to some of any of the embodiments described herein, the samplecomprises oxygen.

According to some of any of the embodiments described herein, aconcentration of dissolved oxygen in the electrolyte is at least 1 ppm.

According to some of any of the embodiments described herein, adetectable concentration of the peroxide-containing compound in thesample is lower than 1 micromolar.

According to some of any of the embodiments described herein, applyingthe potential is performed by linear sweep voltammetry.

According to some of any of the embodiments described herein, the methodfurther comprises, prior to introducing the sample, repetitivelyapplying the potential for at least 5 consecutive times.

According to some of any of the embodiments described herein,repetitively applying the potential is performed such that a portion ofthe metal species is converted to metal particles, the portion being nomore than 50 mol % of the total amount of the metal species.

According to some of any of the embodiments described herein,repetitively applying the potential is performed such that the electrodecomprises no more than 70 mol % of metal species which are metalparticles, of the total amount of the metal in the functional moiety.

According to some of any of the embodiments described herein, thefunctional moiety comprises particles of a metal and ions of the metal,and wherein the repetitively applying the potential is performed suchthat a mol ratio of the ions and the particles ranges from 75:25 to25:75.

According to some of any of the embodiments described herein, theperoxide-containing compound is a peroxide-containing explosive.

According to some of any of the embodiments described herein, theexplosive is selected from the group consisting of TATP, HMDT and TMDD.

According to some of any of the embodiments described herein, the samplefurther comprises hydrogen peroxide.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

Implementation of the method and/or system of embodiments of theinvention can involve performing or completing selected tasks manually,automatically, or a combination thereof. Moreover, according to actualinstrumentation and equipment of embodiments of the method and/or systemof the invention, several selected tasks could be implemented byhardware, by software or by firmware or by a combination thereof usingan operating system.

For example, hardware for performing selected tasks according toembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to embodiments of theinvention could be implemented as a plurality of software instructionsbeing executed by a computer using any suitable operating system. In anexemplary embodiment of the invention, one or more tasks according toexemplary embodiments of method and/or system as described herein areperformed by a data processor, such as a computing platform forexecuting a plurality of instructions. Optionally, the data processorincludes a volatile memory for storing instructions and/or data and/or anon-volatile storage, for example, a magnetic hard-disk and/or removablemedia, for storing instructions and/or data. Optionally, a networkconnection is provided as well. A display and/or a user input devicesuch as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 presents linear sweep voltammetry curves (obtained at a scan rateof 0.1 volt/second) of non-modified CF microelectrode in the presence ofan electrolyte solution containing a mixture of NaOH in deionized water(pH=12) and acetonitrile at 7:3 volume ratio and 0.1 M TBABF₄, withoutTATP addition (black line), upon addition of 20, 40 and 60 ppm of TATP(red, blue and turquoise lines, respectively), and upon addition of 60ppm TATP and 40 ppm H₂O₂(pink line).

FIGS. 2A-2C present linear sweep voltammetry curves (obtained at a scanrate of 0.1 volt/second) of silver benzoate-modified CF microelectrodein the presence of an electrolyte solution containing a mixture of NaOHin deionized water (pH=12) and acetonitrile at 7:3 volume ratio and 0.1M TBABF₄, without HMDT addition (black line), and upon addition of HMDTat the indicated concentrations (FIG. 2A), and upon addition of 180 ppmHMTD and 180 ppm HMTD and 40 ppm H₂O₂ (black and redlines, respectively,in FIG. 2C); The green arrow in FIG. 2A represents the current peaks ofHMTD that were used for the calibration curve (FIG. 2B; ΔI=backgroundcurrent− current peak of HMTD.

FIGS. 3A-3C present scanning electron microscope (secondary electrons(SE) and backscattered electrons (BSE) images (right panels) and X-rayphotoelectron spectroscopy atomic concentrations (left images) of anunmodified CF microelectrode (FIG. 3A), and of a silverbenzoate-modified CF microelectrode after performing one linear sweepvoltammetry scan from 0 volts to −1.6 volts in the electrolyte solution(FIG. 3B) and after performing 100 linear sweep voltammetry scans from 0volts to −1.6 volts in the electrolyte solution (FIG. 3C).

FIGS. 4A-4C present linear sweep voltammetry curves (obtained at a scanrate of 0.1 volt/second) of silver benzoate-modified CF microelectrodein the presence of an electrolyte solution containing a mixture of NaOHin deionized water (pH=12) and acetonitrile at 7:3 volume ratio and 0.1M TBABF₄, performed following 15 subsequent repetitions of linear sweepvoltammetry scans from 0 volts to −1.6 volts, without HMDT addition(black line), and upon addition of HMDT at the indicated concentrations(FIG. 4A), and upon addition of 150 ppm HMTD and 150 ppm HMTD and 40 ppmH₂O₂ (black and redlines, respectively, in FIG. 4C); The green arrow inFIG. 4A represents the current peaks of HMTD that were used for thecalibration curve (FIG. 4B; ΔI=background current−current peak of HMTD.

FIGS. 5A-5C present linear sweep voltammetry curves (obtained at a scanrate of 0.1 volt/second) of silver benzoate-modified CF microelectrodein the presence of an electrolyte solution containing a mixture of NaOHin deionized water (pH=12) and acetonitrile at 7:3 volume ratio and 0.1M TBABF₄, performed following 15 subsequent repetitions of linear sweepvoltammetry scans from 0 volts to −1.6 volts, without TATP addition(black line), and upon addition of TATP at the indicated concentrations(FIG. 4A), and upon addition of 150 ppm TAPT and 150 ppm HMTD and 30 ppmH₂O₂ (black and redlines, respectively, in FIG. 4C); The green arrow inFIG. 4A represents the current peaks of TAPT that were used for thecalibration curve (FIG. 4B; ΔI=background current−current peak of TAPT).

FIG. 6 presents a schematic illustration of an exemplary electrochemicalcell according to some embodiments of the present invention.

FIG. 7 presents linear sweep voltammetry curves (obtained at a scan rateof 0.1 volt/second) of a modified CF microelectrode according toexemplary embodiments of the present invention, in the presence of anelectrolyte solution containing a mixture of NaOH in deionized water(pH=12) and acetonitrile at 7:3 volume ratio and 0.1 M TBABF₄, in thepresence of air (black line) and in the presence of a gaseous samplesaturated with vapors of TATP (red line).

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to detectionof chemicals and, more particularly, but not exclusively, to electrodes,and to systems and methods employing same, usable in electrochemicaldetection of peroxide-based compounds such as peroxide-based explosives.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

In a search for improved systems for electrochemical detection ofperoxide-containing compounds, which feature enhanced selectivity andsensitivity while avoiding complicate and time-consuming procedures, thepresent inventors have recognized that a working electrode which is madeof a flexible material that can be easily and stably modified, and whichcan be manipulated so as to optimize its surface, to thereby increaseits sensitivity, is desirable.

The present inventors have particularly sought for a system that allowsdistinguishing between dissolved oxygen, hydrogen peroxide and otherperoxide-containing compounds so as to perform electrochemical detectionof peroxide-containing compounds in electrolyte solutions whileovercoming the limitations in this methodology associated with thepresence of dissolved oxygen and trace amounts of hydrogen peroxide. Thepresent inventors have recognized that influencing the reduction peaksof oxygen without time-consuming steps (e.g., while circumventing theneed to perform deaeration) can be effected by chemically modifying thesurface of the working electrode.

While conceiving the present invention, the present inventors haveconsidered utilizing carbon electrodes, due to the flexibility of carbonmaterials, and have particularly conceived carbon microfiber electrodeas featuring a morphology that allows suitable signal-to-noise ratio,and which can potentially serve as effective, low cost and sensitivesensor element which meets the strict requirements of detection ofexplosive traces.

The present inventors have conceived that performing chemicaldecomposition of peroxides on the surface of a carbon electrode, whileutilizing a catalyst of such decomposition, would achieve theabove-mentioned goals.

As demonstrated in the Examples section that follows, the presentinventors have indeed designed an electrochemical system which allowssensitive and selective detection of exemplary peroxide-containingexplosives, TATP and HMTD, also in the presence of hydrogen peroxide.The electrochemical system exhibits high sensitivity, allows detectingperoxide-containing compounds at a concentration as low as 250 ppb,allows performing real-time and continuous monitoring ofperoxide-containing compounds, is operated by rapid procedures, whileavoiding time consuming processes of purification and pre-concentration,allows detection within less than seconds, is free of a labeling agent,and thereby circumvents the need to use excitation and imagingtechniques, is easy to integrate with a lab on chipsystem/electrochemical system, can be operated with small volume sample;is reusable; and uses low-cost and low-energy constructions andoperation.

The designed electrochemical system, by being capable of efficientlydetecting peroxide-containing compounds in the presence of dissolvedoxygen and/or hydrogen peroxide, can be utilized, for example, inaqueous environments such as sea water, and in containers, open fields,and any other oxygen-containing environments.

The system can be configured so to feature minimized dimensions,efficient and user-friendly delivery means for introducing the sample tothe system, at the user interface.

Referring now to the drawings, FIG. 6 presents a schematic illustrationof an exemplary set up of an electrochemical cell according to someembodiments of the present invention.

FIG. 1 presents data obtained in linear sweep voltammetry using anon-modified carbon microfiber electrode and show non-separablereduction peaks observed for TAPT and hydrogen peroxide, and fordissolved oxygen.

FIGS. 2A-2C, 4A-4C and 5A-5C present data obtained in linear sweepvoltammetry using a silver-modified carbon fiber microelectrodeaccording to some embodiments of the present invention, and show theseparate reduction peaks observed for TAPT or HMDT, hydrogen peroxide,and dissolved oxygen.

FIG. 7 presents data obtained in linear sweep voltammetry using asilver-modified carbon fiber microelectrode according to someembodiments of the present invention and gaseous sample of TATP, andshow the pronounced reduction peak obtained.

FIGS. 3A-3C presents SEM and XPS measurements of a non-modified CFelectrode and of a silver-modified electrode after one and 100voltammetry cycles, and show a formation of silver nanoparticles on theelectrode-surface upon potential application. As demonstrated in theExamples section that follows, it has been shown that efficientdetection of peroxides is effected upon transformation (conversion) of aportion of the silver ions to silver nanoparticles, which is afforded byrunning several repetitive voltammetry cycles prior to introducing asample to the system.

These data clearly demonstrate that an electrochemical system accordingto the present embodiments enables to perform sensitive, selective,multiplex and high sampling rate detection of peroxide-containingcompounds such as peroxide-containing explosives.

Embodiments of the present invention therefore provide an improvedsensing electrode, and an electrochemical system and method utilizingsame for detecting peroxide-containing compounds in a sample, which areparticularly usable in detecting peroxide-containing compounds in thepresence of dissolved oxygen.

Sensing Electrode:

A sensing electrode according to embodiments of the present inventioncomprises a carbon electrode and a functional moiety in association withat least a portion of a surface of the electrode, the functional moietybeing such that promotes decomposition (e.g., chemical orelectrochemical decomposition) of hydrogen peroxide.

According to some embodiments of the present invention, the carbonelectrode features at least one nanoscale or microscale dimension.

By “microscale dimension” it is meant that at least one dimension of theelectrode is lower than 1 mm, or ranges from 0.1 micron to 900 microns.

By “nanoscale dimension” it is meant that at least one dimension of theelectrode is lower than 1 micron, or ranges from 0.1 nanometer to 900nanometers.

The nanoscale or microscale dimension depends on the shape of theelectrode. If an electrode is generally shaped as a cylinder, the atleast one dimension can be one or both of a length and a diameter of theelectrode. If the electrode is generally shaped as a rectangular, the atleast one dimension can be one or more of a length and a width of theelectrode.

Electrodes featuring one or more microscale or nanoscale dimension(s)are also referred to herein and in the art as microelectrodes.

Carbon electrodes or microelectrodes can be made of glassy carbon,screen-printed carbon, carbon films, carbon fibers, carbon paste, carbonnanoubes, and others.

According to some embodiments of the present invention, the carbonelectrode is a carbon fiber electrode, or a carbon fiber microelectrode(also referred to herein interchangeably as “carbon microfiberelectrode”).

A carbon fiber (CF) electrode is an electrode that comprises elementarycarbon (e.g., graphite) shaped as a fibrous structure (e.g., afilament). Generally, but not necessarily, a CF electrode features amicroscale or even nanosclae diameter or thickness, typically, but notlimited to, in a range of from 1 to 500 microns, or from 5 to 200microns, or from 5 to 100 microns, or from 5 to 50 microns or from 5 to20 microns. Generally, but not necessarily, a CF electrode features alength (height) of from about 100 microns to about 50 mm, or from about100 microns to about 1 mm, or from about 100 microns to about 800microns, including any intermediate values and subranges therebetween.CF electrode featuring at least one dimension in the microscale ornanoscale range is a CF microelectrode.

In some embodiments the CF microelectrode further comprises a mechanicalsupport enveloping or surrounding at least a portion of the electrode,leaving a protruding tip of e.g., from 10 to 100 microns, ofunsupported, exposed portion of the electrode.

The CF microelectrode can be a single-barrel or a multi-barrelelectrode.

In some embodiments, a CF microelectrode is a gas-permeable electrode.Gas permeable electrodes allow sensing of gaseous samples (e.g., air)and/or analytes while circumventing the need to introduce the sample viaa dedicated gas inlet.

By “gas-permeable” it is meant that the electrode is characterized byair permeability through plane higher than 0.3 cfm/ft² through 0.25 mm,when measured according to standard assays such as ASTM 737-96, ISO5636, ISO 4638, ISO 9237, and TAPPI T460.

The CF microelectrodes can be carbon fabric electrodes or carbon paperelectrodes. Carbon fabric electrodes can be made of woven or non-wovencarbon filaments or bundles of filaments. Both electrode types arepreferably gas-permeable electrodes.

Exemplary commercially available gas-permeable carbon fabricmicroelectrodes that are usable in the context of the presentembodiments include, but are not limited to, plain carbon cloth such as,for example, electrodes marketed as ELAT—Hydrophilic Plain Cloth®, 1071HCB plain carbon cloth, Panex 30®.

Exemplary commercially available gas-permeable carbon papermicroelectrodes that are usable in the context of the presentembodiments include, but are not limited to, electrodes marketed byFreudenberg FCCT, such as Freudenberg H23, electrodes of theSpectracarb™ family, Sigracet 39 AA, electrodes marketed under the tradename AvCarb® (e.g., AvCarb P75), and similar gas-permeable carbon paperelectrodes.

Any commercially available CF microelectrode can serve as a raw materialfor providing a CF microelectrode according to the present embodiments,upon generating on at least a part of its surface a functional moiety asdescribed herein.

In some of any of the embodiments described herein, a CF microelectrodeis a carbon paper electrode.

In some of any of the embodiments described herein, the CFmicroelectrode (e.g., the carbon fiber microelectrode) is characterizedby a surface area of at least 10-50 cm² per geometrical cm², includingany intermediate value and subranges therebetween. In some embodiments,the CF microelectrode is electrically connectable to other parts of asensing system via electrically conducting wires, for example,conducting metal foils such as, but not limited to, Ni foils.

The CF microelectrode of the present embodiments features a functionalmoiety, or a plurality of functional moieties, as described herein inany of the respective embodiments, in association with at least aportion of its surface (e.g., an exposed portion of the electrode'ssurface).

By “association with” or “being associated with” and grammaticaldiversions thereof, it is meant that the functional moiety or moietiesare attached to at least a portion of the electrode's surface byphysical and/or chemical means, including physical deposition, physicalabsorption and/or chemical absorption, for example, by means of physicalentrapment or entanglement in or with the carbon fibers, and/or by meansof hydrophobic interactions and/or hydrogen bond interactions and/orother chemical interactions.

In some of any of the embodiments described herein, the CFmicroelectrode features a plurality of functional moieties as describedherein in association with at least a portion of its surface.

In some of any of the embodiments described herein, the functionalmoiety or moieties is/are absorbed to at least a portion of theelectrode's surface.

As defined hereinabove, by “absorbed” it is meant that a functionalmoiety is attached to the surface by physical absorption and/or chemicalabsorption, for example, by means of physical entrapment or entanglementin or with the carbon fibers, and/or by means of hydrophobicinteractions and/or hydrogen bond interactions and/or other chemicalinteractions with the carbon fibers.

In some of any of the embodiments described herein, the functionalmoiety is such that can participate in electrocatalytic reduction ofperoxides.

In some of any of the embodiments described herein, the functionalmoiety promotes decomposition of peroxides by itself and/or is capableof generating (e.g., upon an electrochemical process) a moiety thatpromotes decomposition of peroxides.

As is known in the art, various metal-based materials, including, forexample, silver (Ag), platinum (Pt), palladium (Pd), copper (Cu),iridium (Ir) and gold (Au), as well as iridium (Ir), iron (Fe), copper(Cu), hafnium (Hf), manganese (Mn), gadolinium (Gd), cerium (Ce), lead(Sb), and bismuth (Bi) and metal complexes, metal salts and/or metaloxides thereof, can participate in a catalytic decomposition ofperoxides.

Some of the metal-based materials are active in decomposition ofperoxides when in an elemental, metallic form, some metal-basedmaterials are active when forming a part of a metal complex and/or ametal oxide and/or a metal salt, and some metal-based materials areactive when a combination of elemental metal and a metal complex and/ormetal ions and/or metal oxides is in contact with a peroxide.

Additional examples of metal-based materials that can participate indecomposition of peroxides include, but are not limited to, iron-basedmaterials, such as Fe₂O₃ and organometallic complexes thereof, CuO,HfO₂, CeO₂, Gd₂O₃, manganese dioxide, cobalt oxide, lead oxide, as wellas lead, bismuth, and manganese, including organometallic complexes ofany of the foregoing.

In some of any of the embodiments described herein, the functionalmoiety comprises or is capable of generating, one or more metal speciesthat promote(s) decomposition of peroxides (e.g., electric decompositionof peroxides).

By “metal species” it is meant any metal-containing species, includingelemental metal in a form of, for example, powder, granules, flakes,plates and/or particles, including microparticles and nanoparticles;metal ions (typically cations) which form a part of a metal salt or of ametal complex; metal oxides; metallic complexes, includingorganometallic complexes, of a metal or of a metal ion or of a metaloxide; and any other metal-containing species.

In some of any of the embodiments described herein, the metal speciescomprises ions of a metal that promotes decomposition of peroxide, forexample, electrocatalytic decomposition of peroxides.

In some of any of the embodiments described herein, the metal ions aresuch that undergo reduction to thereby provide elemental metal (e.g., ina form of particles), upon application of a potential in a range of fromabout 0.05 volt to about 2 volt.

Such metal ions generate, upon potential application, metal particlesthat promote (catalyze) decomposition of peroxides, and the overallelectrochemical reaction can be referred to as electrocatalyticdecomposition of peroxides.

Alternatively, the metal species is or comprises elemental metal, whichpromotes as such (as an elemental metal) decomposition of peroxides.

Further alternatively, the metal species is or comprises metals ions,which promote as such (as metal ions) decomposition of peroxides.

Further alternatively, the metal species is or comprises a metal oxide,which promotes as such (as a metal oxide) decomposition of peroxides orwhich can generate elemental metal (e.g., as metal particles) and/ormetal ions, which promote(s) decomposition of peroxides (e.g., uponapplication of potential).

Further alternatively, the metal species is or comprises anorganometallic complex which promotes as such decomposition of peroxidesor which can generate elemental metal (e.g., as metal particles) and/ormetal ions, which promote(s) decomposition of peroxides (e.g., uponapplication of potential).

The present inventors have shown that a functional moiety that comprisesboth particles of a metal that promotes decomposition of peroxides andions of the same metal provides efficient electrochemical sensing ofperoxides.

In some of any of the embodiments described herein, the functionalmoiety comprises both ions and particles of a metal that promotesdecomposition of peroxides, as described herein.

In some of any of the embodiments described herein, the metal speciescomprises both ions and particles of a metal that promotes decompositionof peroxides, as described herein.

In some of any of the embodiments described herein, an amount of themetal particles is no more than 70 mol %, no more than 65 mol %, or nomore than 40 mol % or no more than 30 mol %, of the total amount of themetal species in the functional moiety.

By “mol %” in the context of these embodiments it is meant the number ofmoles of the metal when in a form of elemental metal particles, dividedby the total number of moles of the metal species, that is, the sum ofthe moles of the metal atoms in the functional moiety, namely, the sumof both metal ions and elemental metal particles, multiplied by 100.

Generally, by “mol %” it is meant herein the number of moles of a metalspecies, divided by the total number of moles of the metal atoms, thatis, the sum of the moles of the metal species in the functional moiety,multiplied by 100. The term “mol %” can also be referred to as “atomicconcentration”.

In some of any of the embodiments described herein, an amount of themetal particles is from about 5 mol % to about 65 mol %, of the totalamount of the metal species in the functional moiety (e.g., total numberof moles of both metal ions and metal particles), including anyintermediate values and subranges therebetween.

By “elemental metal” it is meant a metal in its elemental form, that is,a metal species that consists solely of atoms of the metal element. Insome embodiments, the elemental metal features a zero net charge.

In some embodiments, the metal species or the functional moietycomprising same comprises particles of a metal (e.g., elemental metal)and ions of a metal (e.g., derived from a metal salt, a metal oxide or ametal complex), and in some of these embodiments, a mol ratio of themetal ions and the metal particles ranges from 75:25 to 25:75, and canbe, for example, 75:25, 72:28, 70:30, 68:32, 65:35, 62:38, 60:40, 58:42,55:45, 52:48, 50:50, 48:52, 45:55, 42:58, 40:60 38:62, 35:65, 32:68,30:70, 28:72 or 25:75, including any intermediate values and subrangestherebetween.

Without being bound by any particular theory, it has been observed bythe present inventors that when the above-described mol ratio is higherthan 75:25 or lower than 25:75, the electrode is not sufficiently stableand/or its sensing efficiency is reduced.

In some of any of the embodiments described herein, the metal species,or the functional moiety comprising same, further comprises an oxide ofthe metal.

In some of any of the embodiments described herein, the metal species orthe functional moiety comprising same comprises elemental metal (e.g.,as metal particles), metal ions and metal oxides of a metal thatpromotes decomposition of peroxides, as described herein.

Without being bound by any particular theory, it is assumed that metaloxides can be generated on the electrode's surface when the metalparticles or the metal ions contact oxygen present in the environment(e.g., in air or in the electrolyte). The formed metal oxides can alsogenerate metal particles and/or metal ions upon application ofpotential.

In some of any of the embodiments described herein, an amount of themetal oxide is no more than 20 mol %, preferably no more than 15 mol %,or no more than 13 mol %, or no more than 12 mol %, or no more than 10mol %, of the total amount of the metal species in the functional moiety(e.g., the total number of moles of the metal ions, metal particles andmetal oxides in the functional moiety).

In some of any of the embodiments described herein, an amount of themetal oxide ranges from 1 mol % to 20 mol %, of the total amount of themetal species (e.g., the metal ions, particles and oxides in thefunctional moiety), including any intermediate values and subrangestherebetween.

The metal oxide can be a mono-oxide (e.g., MO or M₂O), a di-oxide (e.g.,MO₂ or M₃O₂), a tri-oxide (e.g., MO₃ or M₂O₃), and so forth, dependingon the valency of the metal.

Similarly, a metal ion can be monovalent (M+), divalent (M+²), trivalent(M+³), and so forth, depending on the valency of the metal and on thecounter ion.

M represents a metal, e.g., a metal as described herein.

It is to be noted that according to some of any of the embodimentsdescribed herein, metal oxides and metal ions (e.g., which form a partof a metal salt) are not to be seen as equivalents.

In some of any of the embodiments described herein, the metal oxide isin a form of particles, including microparticles, nanoparticles and acombination thereof.

In some of any of the embodiments described herein, a total amount ofmetal species in a form of particles (e.g., of elemental metal particlesor of metal particles and metal oxide particles) ranges from 20 mol % to70 mol %, of the total number of moles of the metal species (e.g., themetal ions, particles and oxides), including any intermediate values andsubranges therebetween.

In some of any of the embodiments described herein, the metal species orthe functional moiety comprising same comprises particles of bothelemental metal and metal oxides and ions of a metal, and in some ofthese embodiments, a mol ratio of the metal ions and the total amountmetallic particles (of elemental metal and of metal oxide) ranges from75:25 to 25:75, including any intermediate values and subrangestherebetween, and can be, for example, 75:25, 72:28, 70:30, 68:32,65:35, 62:38, 60:40, 58:42, 55:45, 52:48, 50:50, 48:52, 45:55, 42:58,40:60 38:62, 35:65, 32:68, 30:70, 28:72 or 25:75, including anyintermediate values and subranges therebetween.

In some of any of the embodiments described herein, the metal species orthe functional moiety comprising same comprises particles of bothelemental metal and metal oxides and ions of a metal, and in some ofthese embodiments, a mol ratio of the metal ions and the elemental metalis as described herein in any of the respective embodiments, and a molratio of the elemental metal and the metal oxide ranges from 98:2 to50:50, or from 96:4 to 60:40, including any intermediate values andsubranges therebetween, and can be, for example, 98:2, 96:4, 95:5,90:10, 85:15, 80:20, 75:25, 70:30, 68:32, 67:33, 66:34, 65:35, 64:36,63:37, 62:38, 60:40, 55:45 or 50:50, including any intermediate valuesand subranges therebetween.

In some of any of the embodiments described herein, the metal species orthe functional moiety comprising same comprises particles of bothelemental metal and metal oxides and ions of a metal, and in some ofthese embodiments, a mol ratio of the metal ions and the elemental metalis as described herein in any of the respective embodiments, and a molratio of the metal ions and the metal oxide ranges from 10:1 to 4:1, orfrom 90:10 to 80:20, including any intermediate values and subrangestherebetween, and can be, for example, 90:10, 88:12, 85:15, 82:18, or80:20, including any intermediate values and subranges therebetween.

In some of any of the embodiments described herein, the metal species orthe functional moiety comprising same comprises particles of bothelemental metal and metal oxides and ions of a metal, and in some ofthese embodiments the functional moiety or the metal species comprises:Metal ions, in an amount that ranges from 20 mol % to 80 mol %, or from30 mol % to 70 mol %, including any intermediate value and subrangestherebetween, of the total number of moles of the metal atoms in thefunctional moiety or metal species; Elemental metal (e.g., as metalparticles), in an amount that ranges from 10 mol % to 70 mol %, or from20 mol % to 65 mol %, including any intermediate value and subrangestherebetween, of the total number of moles of the metal atoms in thefunctional moiety or metal species; and Metal oxide (e.g., as particles)in an amount that ranges from 1 mol % to 30 mol %, or from 2 mol % to 15mol %, including any intermediate value and subranges therebetween, ofthe total number of moles of the metal atoms in the functional moiety ormetal species.

In some of any of the embodiments described herein, the metal species orthe functional moiety comprising same comprises particles of bothelemental metal and metal oxides and ions of a metal, and in some ofthese embodiments the functional moiety or the metal species comprises:Metal ions, in an amount that ranges from 30 mol % to 70 mol %, or from32 mol % to 62 mol %, including any intermediate value and subrangestherebetween, of the total number of moles of the metal atoms in thefunctional moiety or metal species; Elemental metal (e.g., as metalparticles), in an amount that ranges from 25 mol % to 65 mol %,including any intermediate value and subranges therebetween, of thetotal number of moles of the metal atoms in the functional moiety ormetal species; and Metal oxide (e.g., as particles) in an amount thatranges from 2.5 mol % to 12.5 mol %, including any intermediate valueand subranges therebetween, of the total number of moles of the metalatoms in the functional moiety or metal species.

In some of any of these embodiments, the mol ratio between any two ofthese metal species is as described herein in any of the respectiveembodiments.

In some of any of the embodiments described herein, the metal particlesare metal nanoparticles, having an average size (e.g., diameter) at ananoscale range, as defined herein.

In some embodiments, an average size of the particles ranges from 1nanometer to about 500 nanometers, or from 1 to 200 nanometers, of from1 to 100 nanometers, including any intermediate values and subrangestherebetween. In exemplary embodiments, the average size of the metalparticles is about 40 nanometers.

In some of any of the embodiments described herein, the metal is silver,and the functional moiety comprises silver ions, optionally incombination with silver particles (e.g., silver nanoparticles asdescribed herein) and/or silver oxide.

In some of any of the embodiments described herein, the functionalmoiety comprises an organic moiety that is associated with one or moreof the metal species.

By “associated with” in the context of these embodiments it is meantthat the organic moiety and the metal species are associated with oneanother by physical and/or, preferably, chemical (e.g., covalent,electrostatic, organometallic) interactions.

The organic moiety can be, for example, an organic anion that forms anorganic salt with metal ions; or an organometallic ligand that formswith the metal or a metal oxide or a metal ion an organometalliccomplex.

In some of any of the embodiments described herein, the functionalmoiety is or comprises an organic salt of the metal, which comprises themetal ions (metal cations) and an organic anion.

Without being bound by any particular theory, it is assumed that theorganic anion facilitates the attachment of the metal species to theelectrode's surface, and thereby facilitates the attachment of the metalspecies (e.g., the metal ions and the generated metal particles and/ormetal oxide) to the electrode's surface.

Exemplary organic anions include conjugate bases of organic acids suchas, but not limited to, benzoic acid (benzoate), p-phenyl benzoic acid(p-phenyl benzoate), p-toluene sulfonic acid (p-toluene sulfonate),salicylic acid (salicylate), phenyl acetic acid (phenyl acetate), aceticacid (acetate), trifluoroacetic acid (trifluoroacetate),acetamidobenzoic acid (acetamido benzoate), phthalic acid (phthalate),terephthalic acid (therephthalate), propionic acid (propionate), butyricacid (butyrate), trifluoromethanesulfonic acid(trifluoromethanesulfonate), diethyldithiocarbamic acid(diethyldithiocarbamate), acetyl acetonic acid (acetylacetonate),methane sulfonic acid (methanesulfonate), cycloheane butyric acid(cyclohexanebutyrate), p-toluenesulfonic acid (p-toluenesulfonate),pentafluoropropionic acid (pentafluoropropionate), phthalocyanic acid(phthalocyanate), citric acid (citrate), hexafluoroacetylacetonic acid(hexafluoroacetylacetonate),2,2-Dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionic acid(2,2-Dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionate),sulfadiazine, heptafluorobutyric acid (heptafluorobutyrate),tetrakis(acetonitrile) tetrafluoroboric acid (tetrakis(acetonitrile)tetrafluoroborate), cyanic acid (cyanate), thiocyanic acid(thiocyanate), and fatty acids such as stearic acid (stearate), oleicacid (oleate), lauric acid (laurate), lactic acid (lactate) and more.

In some of any of the embodiments described herein, the metal is silverand the functional moiety is or comprises an organic salt of silver, forexample, silver benzoate.

In some embodiments, the functional moiety is attached to theelectrode's surface by means of physical adsorption, such that, forexample, the metal ions are adsorbed to and/or embedded in themicrofibers forming the electrode.

In some of any of the embodiments described herein, the CF electrodefurther comprises an ion-permeable material attached to at least aportion of its surface.

In some embodiments, the ion-permeable material is a proton exchangemembrane which is permeable to cations but do not conduct anions orelectrons.

Any available proton exchange membrane can be used in the context ofthese embodiments of the invention, including, as non-limiting examples,carbon-based membranes and nickel-based membranes.

In some embodiments, the ion permeable material is a Nafion membrane,preferably a Nafion® Bilayer membrane such as, for example, Nafion® 112,Nafion® 115, Nafion® 117 and Nafion® 119, and any membrane in Nafion®series 900-2000.

Any other ion-permeable material is contemplated.

In some embodiments, the ion-permeable material comprises, or is in aform of, a polymeric film, which is deposited onto the electrode'ssurface (or a portion thereof).

In some embodiments, the film is a thin film, featuring a thickness offrom about 2 nm to about 200 m, including any intermediate values andsubranges therebetween.

In some embodiments, the ion permeable material (e.g., is a form of apolymeric film) is deposited on the same portion of the electrode'ssurface at which the metal ions and/or particles and/or oxides aredeposited.

In some embodiments, the ion-permeable material serves to facilitate thephysical attachment of the functional moiety (the metal species such asmetal ions and metal particles and/or oxides) to the electrode.

In some embodiments, the functional moiety comprising the metal species(e.g., metal ions) and the ion-permeable material are selected such thatthe functional moiety physically interacts with the ion-permeablematerial.

Herein, “physical attachment”, “physical interaction” and grammaticaldiversions thereof describe interactions which do not involve chemicalcovalent or electrostatic bonds, and include interactions such asabsorption (possibly via hydrogen bonds and/or hydrophobicinteractions), entrapment, entanglement, incorporation, coating or anyother interaction that leads to interconnection between the indicatedsubstances.

Without being bound by any particular theory, the functional moiety andthe ion-permeable material are selected such that the functional moiety(e.g., the metal species) does no penetrate membrane pores of theion-permeable material, and thus remains attached to the electrode.

A sensing electrode as described herein in any of the respectiveembodiments, is also referred to interchangeably as a modified CFelectrode, or a modified CF microelectrode, or silver-modified CFelectrode, or silver-modified CF microelectrode and diversions andvariations thereof.

Sensing System:

In some of any of the embodiments described herein, the sensingelectrode as described herein is usable for electrochemical detection ofa peroxide-containing compound in a sample.

In some of any of the embodiments described herein, the sensingelectrode as described herein is usable for electrochemicallydetermining a presence and/or level of a peroxide-containing compound ina sample.

In some of any of the embodiments described herein, the sensingelectrode as described herein is usable for determining a presenceand/or level of a peroxide-containing compound in a sample, uponintegrating the electrode in an electrochemical cell.

In some embodiments of the present invention, there is provided anelectrochemical cell which comprises a sensing electrode as describedherein in any of the respective embodiments and any combination thereof.The sensing electrode functions as a working electrode.

In some embodiments of the present invention, there is provided asensing system which comprises a sensing electrode as described hereinin any of the respective embodiments and any combination thereof. Such asensing system is also referred to as a sensor.

In some embodiments of the present invention, there is provided asensing system which comprises an electrochemical cell as describedherein in any of the respective embodiments and any combination thereof.

The following describes some embodiments of an electrochemical cell ofthe invention.

In some of any of the embodiments described herein, the sensingelectrode is electrically connectable to a power source, and the cell isconfigured such that when it is operated, at least a portion of thesensing electrode, i.e., a portion thereof that have functional moietiesas described herein deposited on the electrode's surface), contacts theanalyte (a peroxide-containing compound or a sample containing same).

In some embodiments of the present invention, the electrochemical cellfurther comprises a reference electrode. Any commercially available orcustomarily designed reference electrode is contemplated.

In some of any of the embodiments described herein, the referenceelectrode is an aqueous reference electrode. Exemplary usable referenceelectrodes include, but are not limited to, Silver/Silver Chlorideelectrode (e.g., Ag/AgCl/Saturated KCl electrode such as marketed byMetrohm), a Standard calomel (e.g., saturated calomel) electrode (SCE),a Standard hydrogen electrode (SHE), a Normal hydrogen electrode (NHE),a Reversible hydrogen electrode (RHE), a Copper-copper(II) sulfateelectrode (CSE); a pH-electrode; a Palladium-hydrogen electrode, aDynamic hydrogen electrode (DHE), and a Mercury-mercurous sulfateelectrode (MSE).

The reference electrode is also electrically connectable to a powersource, and the cell is configured such that when it is operated, apotential difference (voltage) is applied between the sensing electrodeand the reference electrode.

In some embodiments, the electrochemical cell follows a three-electrodedesign and further comprises an auxiliary electrode. Preferably, but notobligatory, the auxiliary electrode is also a carbon electrode,preferably a glassy carbon electrode. Any other auxiliary electrode,commercially available or customarily designed, is contemplated.Non-limiting examples include gold electrodes, other carbon electrodes,platinum electrodes and carbon/gold electrodes.

In some embodiments, the auxiliary electrode is electrically connectableto the sensing electrode.

In some of any of the embodiments described herein, the electrochemicalcell further comprises a device that measures a current generated at thesensing electrode, as a result of redox reactions occurring at or nextto a surface of the sensing electrode. In some embodiments, this device(e.g., an amperometer, a picoameter) is electrically connectable to theauxiliary electrode and the sensing electrode.

A schematic presentation of an exemplary assembly of a three-electrodeelectrochemical cell 10 according to some embodiments of the presentinvention is presented in FIG. 6.

Electrochemical cell 10 comprises a sensing electrode 12 as describedherein, which acts as a working electrode. Sensing electrode 12 featuresfunctional moieties 16 as described herein (e.g., metal ions such assilver ions as described herein, optionally in combination with metalparticles and/or metal oxides, as described herein, and optionally anion-permeable material as described herein) at least on a portion of asurface thereof. When the cell is operated, the portion of the electrodethat features functionalized moieties 16 should be in contact with theanalyte, e.g., by contacting an electrolyte 18 in which the analyte isdissolved. Sensing electrode 12 is one half of electrochemical cell 10.A reference electrode 22 is the other half of cell 10. A power source 20is electrically connectable to sensing electrode 12 and referenceelectrode 22 by means of electrical wires 24. Power source 20 isconfigured to apply voltage between sensing electrode 12 and referenceelectrode 22, for example, by applying potential to one of theelectrodes. Optionally, but not obligatory, cell 10 further comprises anauxiliary electrode 26, and a current measuring device 28, and device 28is electrically connectable to sensing electrode 12 and auxiliaryelectrode 26.

For an electrochemical cell (e.g., cell 10) to operate, at least thesensing electrode (electrode 12) should be in contact with anelectrolyte solution shown in FIG. 6 as an electrolyte solution 18. Theelectrochemical cell (e.g., cell 10) can comprise an electrolytesolution (e.g., electrolyte solution 18, as exemplified in FIG. 6), orcan comprise means (e.g., an inlet port; not shown in FIG. 6), forintroducing the electrolyte to the cell, so as to contact at least thesensing electrode (e.g., sensing electrode 12).

An electrochemical cell according to the present embodiments can followany of the designs known in the art, and can include one or more sensingelectrodes, and one or more of a reference electrode and/or an auxiliaryelectrode. Exemplary designs include, without limitation, rotatingdisk-ring electrodes, ultramicro-electrodes, or screen printedelectrodes.

The configuration of the components of electrochemical cell 10 aspresented in FIG. 6 are for illustrative purpose only and are not to beregarded as limiting in any way.

Electrochemical cell 10 can be, for example, in a form of a coveredglass (or other inert material like Teflon or quartz) beaker, containingthe sample solution in which the three electrodes are dipped. In someembodiments, electrochemical cell 10 is a micro cell or a thin layercell.

Electrochemical cell 10 may further comprise means for mixing/stirring asample with electrolyte 18 (not shown in FIG. 6).

Electrochemical cell 10 may further comprise means for monitoring and/orcontrolling the temperature inside the cell (not shown in FIG. 6).

As used herein and in the art, an electrolyte is an electricallyconducting material or medium. An electrolyte can be solid or fluid, andcan be used per se or when dissolved in a polar solvent, such as water.When dissolved is a solvent, it is referred to as an electrolytesolution. In the context of electrochemical cells, an electrolyte isalso referred to as a background solution.

Herein throughout, the term “electrolyte” also encompasses an“electrolyte solution”, unless specifically indicated otherwise.

In an electrochemical cell as described herein (e.g., cell 10, FIG. 6),at least the sensing electrode (e.g., sensing electrode 12) contacts theelectrolyte solution (e.g., electrolyte solution 18) when the cell isoperated. In some embodiments, all electrodes contact an electrolytesolution (e.g., electrolyte solution 18) when the cell is operated. Insome embodiments, all electrodes contact the same electrolyte solution,as exemplified in FIG. 6, and in some embodiments, one or more of theelectrodes contact an electrolyte solution different from theelectrolyte solution in contact with the sensing electrode, and amembrane is interposed between the different electrolyte solutions.

In some of any of the embodiments described herein, the electrolytesolution (e.g., electrolyte solution 18, FIG. 6), features an alkalinepH, that is, a pH higher than 7, or higher than 7.4, or higher than 8,or higher than 10, or higher than 11, for example, pH 12, or higher.

In some of any of the embodiments described herein, the electrolytesolution (e.g., electrolyte solution 18, FIG. 6), features a pH in arange of from 8 to 14, or from 8 to 13, or from 8 to 12, or from 10 to14, or from 10 to 13, or from 10 to 12.

In some of any of the embodiments described herein, the electrolytesolution (e.g., electrolyte solution 18, FIG. 6) is or comprises anaqueous solution, e.g., an alkaline aqueous solution, featuring a pH asdescribed herein.

In some of any of the embodiments described herein, the electrolytesolution (e.g., electrolyte solution 18, FIG. 6) comprises a mixture ofan aqueous solution and an organic solvent.

Exemplary alkaline aqueous solutions include aqueous solutions of watersoluble alkaline substances, for example, metal alkali hydroxides suchas sodium hydroxide, potassium hydroxide, or of metal-earth hydroxides,such as magnesium hydroxide or calcium hydroxide. Exemplary alkalineaqueous solutions include also a buffer solution that provides thedesired pH value, as described herein. Buffer solutions that provide analkaline pH as described herein are well known to those skilled in theart.

Exemplary organic solvents include water-miscible solvents, preferablypolar and/or aprotic solvents, and, further preferably, in which theperoxide-containing solvent is dissolvable and/or in which an organicquaternary ammonium salt of choice, as described herein, is dissolvable.

Suitable organic solvents are preferably further characterized ascapable of inhibiting or reducing electrolysis of water and/or ofbroadening the electrochemical window of water, for example, up to −2Volts.

Suitable organic solvents are preferably further characterized as beingchemically compatible with (e.g., chemically inert to) theelectrochemical cell or system as described herein. In some embodiments,the organic solvent is characterized as being chemically compatible withplastic and/or any other polymeric or glassy materials typically usedfor constructing electrochemical cells or systems.

An exemplary solvent is acetonitrile, although other solvents, such as,for example, dimethyl formamide, dimethylsulfoxide, propylene carbonate,ethanol, methanol, N-methylpyrrolidone, tetrahydrofuran, ethyl acetate,acetone, dimethyl ether, pyridine, diethyl ether, hexamethylphosphorictriamide, and hexamethylphosphorous, and any mixture thereof, arecontemplated. Another exemplary solvent is ethanol.

A volume ratio between an aqueous solution and an organic solvent canrange, for example, from 10:1 to 1:1, or from 5:1 to 1:1, or from 3:1 to1:1, or from 5:1 to 3:1, including any intermediate value and subrangestherebetween. For example, an electrolyte solution can comprise 90 vol.% aqueous solution and 10 vol. % organic solvent, or 80 vol. % aqueoussolution and 20 vol. % organic solvent, 75 vol. % aqueous solution and25 vol. % organic solvent, or 70 vol. % aqueous solution and 30 vol. %organic solvent, or 65 vol. % aqueous solution and 35 vol. % organicsolvent, or 60 vol. % aqueous solution and 60 vol. % organic solvent, or55 vol. % aqueous solution and 45 vol. % organic solvent, or 50 vol. %aqueous solution and 50 vol. % organic solvent. In some embodiments, anelectrolyte solution comprises 70 vol. % aqueous solution and 30 vol. %organic solvent.

In some of any of the embodiments described herein, an electrolytesolution (e.g., electrolyte solution 18, FIG. 6), comprises a solublesalt (e.g., a water-soluble salt, or a salt soluble in the solventmixture making up the electrolyte solution). Any soluble salt commonlyused in electrolyte solution for increasing the ionic strength iscontemplated, typically an inorganic salt, with potassium chloride beinga non-limiting exemplary salt. A concentration of the salt typicallydetermines, at least in part, the ionic strength of the electrolytesolution and can range from, for example, 0.1M to 1M, or from 0.1M to0.5M, including any intermediate value and subranges therebetween.

In some embodiments, a concentration of the salt is 0.25M.

In some of any of the embodiments described herein, the electrolytesolution comprises a quaternary ammonium salt, preferably, an organicquaternary ammonium salt. An organic quaternary ammonium salt can berepresented by the Formula:

R₁R₂R₃R₄N⁺X⁻

wherein: R₁, R₂, R₃ and R₄ is each independently an alkyl, cycloalkyl oraryl, or alternatively, two or more form together a heterocylic(heteroalicyclic or heteroaryl) ring; and X is an anion such as halide,(e.g., chloride, bormide, iodide), perchlorate, borate, and any otheracceptable anion.

The selection of the anion can be made such that it is inert to theelectrochemical window of water, that is, the anion is preferably suchthat features a standard electrode potential higher than hydroxide.

In some embodiments, the anion is other than halide.

In some embodiments, R₁, R₂, R₃ and R₄ is each independently an alkyl,and in some embodiments, each is independently an alkyl of from 1 to 4carbon atoms.

In some of any of the embodiments described herein, the organicquaternary ammonium salt is soluble in the electrolyte solution asdescribed herein in any of the respective embodiments.

Exemplary organic quaternary ammonium salts that are usable in thecontext of the present embodiments include commonly used phase transfercatalysts.

In some of any of the embodiments described herein, a concentration ofthe quaternary ammonium salt is lower than 0.5 M, or lower than 0.2M, orlower than 0.1 M. In some embodiments, a concentration of the quaternaryammonium salt ranges from 1 to 10 mM, including any intermediate valuesand subranges therebetween. In some embodiments, a concentration of thequaternary ammonium salt is 5 nM.

In some of any of the embodiments described herein, the quaternaryammonium salt is such that assists in providing a sharp peak of theoxygen reduction and/or of the peroxide reduction.

Non-limiting examples of a quaternary ammonium salt includetetrabutylammonium iodide and tetrabutylammonium perchlorate, althoughother quaternary ammonium compounds are contemplated.

An exemplary electrolyte solution according to the present embodimentsin described in the Examples section that follows. As exemplifiedtherein, an electrolyte solution comprising a mixture of an aqueous NaOHsolution, having pH 12, an organic solvent, and an organic quaternaryammonium salt at a low concentration, when used in combination with asensing electrode as described herein, enables to separate the reductionpeaks generated in the presence dissolved oxygen and also of hydrogenperoxide and allows performing electrochemical detection whilecircumventing the need to deaearate (e.g., evacuate oxygen from) thecell or system, and while overcoming faults caused by interference oftraces of hydrogen peroxide that are typically present inperoxide-containing compounds.

In some of any of the embodiments described herein, an electrochemicalcell and/or a sensing system comprising same, as described herein, isoperable when a concentration of oxygen in the electrolyte is at least 1ppm, or at least 10 ppm, or at least 20 ppm, or at least 30 ppm, orhigher.

In some of any of the embodiments described herein, electrochemicaldetection of a peroxide-containing compound is performed using anelectrochemical cell and/or a sensing system comprising same, asdescribed herein, when a concentration of oxygen in the electrolyte isat least 1 ppm, or at least 10 ppm, or at least 20 ppm, or at least 30ppm, or higher.

In some of any of the embodiments described herein, an electrochemicalcell and/or a sensing system comprising same, as described herein, isoperable when a concentration of oxygen in the electrolyte is higherthan a concentration of a peroxide-containing compound in theelectrolyte by at least 10-folds, or at least 20 folds, or at least30-folds, or at least 50-folds or at least 100-folds, or at least1000-folds or at least 5000-folds, and even higher.

In some of any of the embodiments described herein, electrochemicaldetection of a peroxide-containing compound is performed using anelectrochemical cell and/or a sensing system comprising same, asdescribed herein, when a concentration of oxygen in the electrolyte ishigher than a concentration of a peroxide-containing compound in theelectrolyte by at least 10-folds, or at least 20 folds, or at least30-folds, or at least 50-folds or at least 100-folds, or at least1000-folds or at least 5000-folds, and even higher.

In some of any of the embodiments described herein, the sensing systemand/or the electrochemical cell described herein is/are devoid of meansfor deaerating the system or cell prior to contacting the sensingelectrode with a sample. Such means typically include physical means forintroducing an inert gas, such as argon gas or nitrogen gas, to thecell, and optionally a source of the inert gas connectable to the means;and/or means for chemically removing oxygen, for example, zinc or sodiumsulfate.

In some of any of the embodiments described herein, the sensing systemand/or the electrochemical cell described herein is/are devoid of meansfor bubbling an inert gas in the electrolyte solution and/or means forconnecting the cell and/or the system to a source of an inert gas.

In some of any of the embodiments described herein, the sensing systemand/or the electrochemical cell described herein is/are devoid of zinc,sodium sulfate, or any other chemical reagents that can react withoxygen; and/or is/are devoid of means of contacting oxygen with suchchemical reagents.

In some of any of the embodiments described herein, a system asdescribed herein further comprises means for introducing a sample to theelectrochemical cell. The sample should be introduced to the cell suchthat it contacts the sensing electrode.

In some embodiments, the sensing system comprises means for introducinga sample to the electrochemical cell such that it contacts the sensingelectrode.

In some embodiments, the sensing system comprises means for introducinga sample to the electrochemical cell such that it is mixed with ordissolved in the electrolyte solution.

In some embodiments, a sample is introduced to the electrochemical cellby means of an inlet port, referred to herein also as a sample inlet. Insome embodiments, the inlet port is configured for introducing a gaseoussample to the cell. In some embodiments, the inlet port is configuredfor introducing a liquid sample to the cell. In some embodiments, afluid (gaseous and/or liquid) sample is bubbled into the electrolytesolution and the inlet port is configured for effecting such bubbling.

In some of any of the embodiments described herein, the system is devoidof a sample inlet. This is enabled by the carbon fiber electrode, whichis gas permeable and hence gas samples can enter the electrochemicalcell therethrough.

In some of any of the embodiments described herein, the means forintroducing a sample to the electrochemical cell include a pump or apumping device. An exemplary pump is an air pump, in cases where thesample is in a gaseous form. The pump or the pumping device can be incontact with the CF microelectrode of the present embodiments, such thatthe pumped sample permeates through the electrode and is thus introducedto the cell or system. Alternatively, the pump or pumping device are incontact with the electrolyte, such that the pumped sample contacts or ismixed with the electrolyte.

In some of any of the embodiments described herein, a system asdescribed herein further comprises a gas outlet.

In some of any of the embodiments described herein, a sensing system asdescribed herein is operable by assembling at least a sensing electrodeas described herein and an electrolyte solution, and electric means forelectrically connecting the sensing electrode to a power source;introducing a sample into the electrochemical cell, by means that allowthe sample to contact (e.g., dissolve in) the electrolyte solution, asdescribed herein; electrically connecting the sensing electrode to thepower source; applying a potential to the sensing electrode, by means ofa power source as described herein; and measuring an electrochemicalsignal that is indicative of an electrochemical reaction in which theperoxide-containing compound participates.

In some of any of the embodiments described herein, the electrochemicalsignal is an electrical current generated at the sensing electrode isresponse to said potential, and measuring the signal is effected bymeans of an electrical current measuring device.

The measured current is indicative of a presence and/or level (e.g.,amount, concentration) of a peroxide-containing compound in the sample.

In some of any of the embodiments described herein, the electrochemicalcell comprises a reference electrode and applying a potential iseffected by applying voltage between the sensing electrode and thereference electrode.

In some of any of the embodiments described herein, the power source isconfigured to apply potential to the sensing electrode according to anyknown voltammetry method, as described in further detail hereinafter, inembodiments related to a sensing method.

In some embodiments, the power source is configured to apply a varyingpotential to the sensing electrode, and in some embodiments, the powersource is configured to apply a linearly varying potential (as in linearsweep voltammetry); a staircase varying potential; a squarewave varyingpotential; or a pulse varying potential (normal pulse or differentialpulse), as described in further detail hereinbelow.

In some embodiments, the power source is configured to apply a varyingpotential to the sensing electrode in a linear sweep mode.

In some of any of the embodiments described herein, the system isconfigured such that the functional moiety comprises metal ions andmetal particles and/or metal oxides, as described herein in any of therespective embodiments.

In some of any of the embodiments described herein, the system isconfigured such that upon potential application, a portion (e.g., lessthan 70 mol %, or less than 60 mol %, or less than 50 mol) of totalamount of the metal species initially deposited on the electrode'ssurface (e.g., metal ions) is converted to metal particles.

In some of any of the embodiments described herein, the functionalmoiety comprises metal ions and the system is configured such that uponapplication of a potential, a portion of the metal ions, as describedherein, is converted into metal particles.

In some of any of the embodiments described herein, the system isconfigured such that upon potential application, the functional moietycomprises metal particles in an amount that ranges from 20 mol % to 70mol % of the total number of moles of metal species in the functionalmoiety, as described herein in any of the respective embodiments.

In some of any of the embodiments described herein, the system isconfigured such that the functional moiety comprises particles of ametal and ions of the same metal, and a mol ratio of the ions of themetal and the particles of the metal ranges from 75:25 to 25:75 or from70:30 to 30:70, as described herein in any of the respectiveembodiments.

In some of any of the embodiments described herein, system is configuredsuch that upon potential application, the functional moiety comprisesparticles of a metal and ions of the same metal, and oxide of the samemetal, and a mol ratio of the ions of the metal and the particles of themetal, or of the ions of the metal and the total amount of metalparticles (e.g., particles of elemental metal and of the metal oxide),or of the metal ions and the metal oxide or of the elemental metal andthe metal oxide are as described herein in any of the respectiveembodiments.

In some of any of the embodiments described herein, the system isconfigured such that upon potential application, the functional moietycomprises particles of a metal and ions of the same metal, and oxide ofthe same metal, each in an amount as described herein in any of therespective embodiments.

In some of any of the embodiments described herein, the system isconfigured to determine a current generated in response to the varyingpotential, and in some embodiments, the system is configured fordetermining a change in the current generated at the sensing electrode,in response to the varying potential.

In some of any of the embodiments described herein, the system isconfigured to determine an electric current or a change in an electriccurrent, compared to an electric current or a change in the electriccurrent generated at the sensing electrode, in response to the varyingpotential, when a sample is not introduced to the electrochemical cell.Such data is also referred to herein as “background current, and in someembodiments, the system is configured to subtract the background currentfrom the determined current or change in current.

In some embodiments, the system is operable in a linear sweepvoltammetry mode and is configured to determine a change in anelectrical current in response to a linear change in the potential, asis known in the art.

Generally, but not necessarily, the system is configured for providing avoltammogram that presents values that are in line with the voltammetrymethodology used.

Determination of an electrical current, or a change in an electricalcurrent, according to any of the respective embodiments, can beperformed by means of a device which is configured to process thereceived signals (e.g., the mode of the applied varying potential andcorresponding generated current data) so as to provide a value or a setof values as desired (e.g., a change in electrical current relative tothe applied potential, or any other voltammogram). Such a device is alsoreferred to herein as a signal processor.

In some of any of the embodiments described herein, the signal processoris a data processor such as a computer configured for receiving andanalyzing the signals. The signal processor extracts, from eachgenerated signal or set of signals, a parameter (e.g., a voltammogram)that is indicative of an electrochemical reaction of aperoxide-containing compound, and hence of a presence and/or level ofthe peroxide-containing compound.

In some embodiments of the invention the signal processor is configuredto construct a fingerprint of a peroxide-containing compound, forexample, a voltammogram obtained upon contacting an electrolyte solutionwith the peroxide-containing compound and applying a certain mode of avarying potential (e.g., a linear sweep potential).

In some embodiments of the invention the signal processor is configuredto construct a database of fingerprints of a plurality ofperoxide-containing compounds, for example, a database of voltammogramsobtained upon contacting an electrolyte with a peroxide-containingcompound and applying a certain mode of a varying potential (e.g., alinear sweep potential). The database can include several voltammogramsfor each peroxide-containing compound, each for a different mode and/orrange and/or rate of application of the varying potential, and/or eachfor a different electrolyte.

In some embodiments of the invention the signal processor is configuredto search a database of fingerprints of a plurality ofperoxide-containing compounds, for example, a database of voltammogramsas described herein, for a fingerprint that matches a receivedfingerprint, and to identify accordingly the peroxide-containingcompound.

In some of any of the embodiments of the invention the signal processoris configured to determine a level of an identified peroxide-containingcompound in a sample, by accessing and/or processing relevant data. Suchdata can include, for example, a calibration curve, e.g., ofvoltgammograms, or of specific values obtained in voltammetrymeasurements (e.g., a reduction peak), obtained for varyingconcentrations of the identified peroxide-containing compound, andstored on a computer readable medium. For example, the signal processormay access the calibration curve, search for a value (e.g., a reductionpeak) that matches the value obtained upon operating the system, andidentify a concentration of the identified peroxide-containing compoundthat matches this value. Alternatively, or in addition, the data includea lookup table stored on a computer readable medium, which can besearched for values that match the measured value and are indicative ofa level of an identified peroxide-containing compound. Furtheralternatively, or in addition, the data include a predeterminedrelationship between the measured value and a level of the identifiedperoxide-containing compound. For example, if such a predeterminedrelationship comprises a linear relationship, the signal processor candetermine the level of an identified peroxide-containing compound bymeans of extrapolation, based on the pre-determined relationship.

In some of any of the embodiments described herein, the sensing systemas described herein further comprises an additional sensing electrode,which is configured to generate an electrical signal upon contacting acompound other than a peroxide-containing compound. In some of theseembodiments, the additional sensing electrode forms a part of anadditional electrochemical cell. Such a system is configured such that asample is introduced therein and contacts both sensing electrodes. Thegenerated electrical signals are thus indicative of the presence/absenceand amount (if present) of both the peroxide-containing compound and theother compound.

In some embodiments, such a sensing system further comprises a signalprocessor as described herein which is configured to identify theperoxide-containing compound, as described herein, and to identify theother compound, and, optionally, to further determine a level of eachidentified compound in a sample.

In some embodiments, the additional sensing electrode is a carbonelectrode which is modified so as to detect the additional compound.

In some embodiments, the additional sensing electrode is configured todetect explosives other than peroxide-containing explosives, forexample, nitro-containing compounds.

In some of any of the embodiments described herein, a sensing system asdescribed herein comprises a plurality (e.g., two, three or more) ofmodified CF microelectrodes as described herein, wherein at least oneportion of the CF microelectrodes is modified so as to feature a firstfunctional moiety and at least another portion of the CF microelectrodesfeatures a second functional moiety which is different from the firstfunctional moiety, whereby both functional moieties interact with aperoxide-containing material as described herein in any of therespective embodiments.

In some of these embodiments the sensing system comprises three, four ormore portions of CF microelectrodes, each featuring a differentfunctional moiety that interacts with a peroxide-containing compound asdescribed herein.

In some of any of these embodiments, the sensing system comprises aplurality of electrochemical cells or a plurality of electrochemicalhalf cells, each being individually connectable to a power source, and,optionally, each being individually connectable to a device formeasuring the electrochemical parameter as described herein.

In some of any of these embodiments, each of the measuring devices canindependently be connected to a signal processor, or, alternatively, allmeasuring devices are connected to the same signal processor.

Such a sensing system can generate for different peroxide-containingcompounds different defined fingerprints, and allows using, for example,a dedicated database, for the identification of the peroxide-containingcompound based on such fingerprints database, according to theguidelines provided herein.

Electrochemical Detection:

According to an aspect of some embodiments of the present inventionthere is provided a method of detecting a peroxide-containing compoundin a sample, while utilizing a sensing electrode as described herein inany of the respective embodiments.

In some embodiments, a method as described herein utilizes a sensingelectrode and an electrolyte solution, as described herein in any of therespective embodiments. In some embodiments, a method as describedherein utilizes a sensing system, as described herein in any of therespective embodiments.

In some embodiments, a method as described herein is devoid of a step ofdeaerating the electrolyte or a cell or a system comprising theelectrolyte prior to performing the detection.

In some embodiments, a method as described herein is performed when aconcentration of dissolved oxygen in the electrolyte at the time ofdetection is at least 1 ppm, and/or is higher by at least one order ofmagnitude than a concentration of the peroxide-containing compound inthe electrolyte, as described herein.

Herein throughout, the terms “detection”, “detecting” and grammaticaldiversions thereof, and the terms “sensing”, are used interchangeably,and refer to determining a presence and/or level of aperoxide-containing compound.

In some of embodiments, the method as described herein is a method ofelectrochemical detection of peroxide-containing compounds.

In some embodiments, the method is effected by contacting a sensingelectrode as described herein in any of the respective embodiments witha sample, and applying a potential to the sensing electrode.

In some embodiments, the method is further effected by measuring anelectrochemical parameter upon applying the potential to the sensingelectrode, and in some embodiments, the electrochemical parameter is anelectrical current generated at the sensing electrode or a change in theelectrical current at the sensing electrode. A presence and/or level ofthe electrochemical parameter is indicative of a presence and/or levelof the peroxide-containing compound.

In some embodiments, the sensing electrode forms a part of anelectrochemical cell as described herein in any of the respectiveembodiments, or a part of a sensing system as described herein in any ofthe respective parameters, and contacting the sensing electrode with thesample is effected by introducing the sample to the electrochemical cellor system, as described herein.

The sample can be introduced to the cell or system by means of a sampleinlet, or by means of a pump, as described herein.

In some embodiments, contacting the sensing electrode with the sample iseffected by introducing the sample to an electrolyte solution,preferably an electrolyte solution as described here in any of therespective embodiments.

In some embodiments, contacting the sensing electrode with the sample iseffected by contacting a gas permeable sensing electrode with a gaseoussample for example, by means of an air pump as described herein.

In some embodiments, the electrolyte and the sensing electrode form apart of an electrochemical cell or sensing system as described herein,and in some of these embodiments, the sensing electrode contacts theelectrolyte.

In some embodiments, the method further comprises contacting the sensingelectrode with the electrolyte, either prior to or subsequent tointroducing the sample to the electrolyte.

In some embodiments, applying a potential to the sensing electrode isperformed immediately after contacting the sensing electrode with thesample.

In some embodiments, applying a potential to the sensing electrode isperformed immediately after contacting the sensing electrode with thesample.

In some embodiments, applying a potential to the sensing electrode isperformed immediately after contacting the sensing electrode with anelectrolyte to which the sample was introduced.

In some embodiments, applying the potential is performed while aconcentration of dissolved oxygen in the electrolyte is at least 1 ppm,as described herein.

In some embodiments, the sensing electrode forms a part of anelectrochemical cell as described herein and applying the potential isperformed by applying a voltage between the sensing electrode and areference electrode.

In some embodiments the potential is a varying potential.

In some embodiments, measuring an electrochemical parameter is by avoltammetry experiment.

As known in the art, voltammetry experiments are conducted for obtaininginformation (e.g., presence, identity and/or level) of an analyte bymeasuring a generated current or a change in the current in response toapplication of a varying potential.

In order to obtain a quantitative measurement of an analyte (e.g., aperoxide-containing compound as described herein) by potentiostaticelectrochemical analysis, the amount of electrons used for the reductivedecomposition of the analyte should be monitored. In thermodynamicequilibrium the ratio of the redox-reactive species at the surface ofthe electrode can be obtained by Nernst equation:

$E = {E^{0} + {\frac{2.3\; {RT}}{nF}{\log \left( \frac{C_{O}}{C_{R}} \right)}}}$

Where Co is the concentration of the oxidized form, and C_(R) is theconcentration of the reduced form, E is electrode potential, E⁰ isstandard electrode potential, R is the gas constant

$\left( {8.314\; \frac{J}{Kmol}} \right),$

T is the temperature (Kelvin scale), n is the number of electronsparticipate in the redox reaction and F is the Faraday constant (96,487coulombs).

The entire measured current is composed of Faradic currents andnon-Faradaic charging background current. The Faradic current obtainedby the electrochemical reaction behaves according to Faraday's low,which means that 1 mole of redox active substance will involve a chargechange of n×96,487 coulombs.

The information retrieved by voltammetry experiments, in its simplestform, is obtained as a voltammogram of I=f(E).

A voltammogram is a current versus potential curve used to describe theanalyte's electrochemical reaction performed at the electrode as aresult of the applied potential, and its derived current. It may have acomplicated multi-stepped shape according to the complexity of thechemical reaction.

In some embodiments, and depending on the type of voltammetry used, thepotential is varied continuously or stepwise or in pulses.

In some embodiments, the potential or varying potential applied to thesensing electrode is such that allows reductive decomposition of theperoxide-containing compound.

Exemplary potentials that can be applied to a sensing electrode asdescribed herein range from 0 to about −2 Volts.

Voltammetry experiments can be categorized as linear sweep voltammetryand cyclic voltammetry.

Cyclic voltammetry is the process of electrochemical analysis in whichthe applied voltage is of a multi or mono-triangular shape. Theresulting plot of current versus linear triangular potential scan of theworking electrode is called cyclic voltammogram, while the plot ofcurrent versus linear potential scan of the working electrode is calledlinear sweep voltammogram. Cyclic voltammetry is usually the preliminaryprocess used to determine the reduction potential of an analyte, themedia's influence and the thermodynamics, as well as kinetics, of theelectrochemical reaction.

In response to the triangular shaped potential, the measured current ofthe electrochemical cell that contained initially only the oxidizedspecies, gradually increases up to a sharp peak at E_(p[red]), followedby current decrease when most species adjacent to the electrode surfaceare reduced. When reversing the potential's direction, a gradualincrease of current at the opposite direction ends in a sharp peak atE_(p[ox]), where the chemical reaction proceeds to the oppositedirection towards the oxidized form. When most species adjacent to theelectrode surface are oxidized, the current decreases until the point ofpotential reverses, and so on.

Since an electrochemical reaction is located at the interface betweenthe working electrode and the electrolyte solution, the reduced andoxidized species causing the sharp peaks of the voltammogram areconcentrated to a narrow diffusive layer adjacent to the electrode. As aresult, the shape of the curve's peak depends on the rate of diffusion.The peak's incline correlative to the concentration of electroactiveparticles on the electrode's surface, while the sharp decline dependssolely on time, and results from the absence of electroactive particlesnear the surface due to limited diffusion.

In order to increase the sensitivity of voltammetric measurements, theshare of the Faradic currents in the obtained voltammogram can beincreased on the expense of the non-faradaic background current. Suchalterations are enabled by applying a series of short duration potentialsteps (each last for several milliseconds) in a technique termed “pulsevoltammetry”. At the end of each potential step, two different currentdecay rates are obtained: sharp exponential decay to a negligible levelis characteristic to the charging current, while slower decay is typicalto the Faradic current. By recording the current's signal at the laterregime, more of the signal is attributed to the Faradic current, whilethe contribution of the charging current is negligible. The differentialpulse voltammogram is obtained from the subtraction of the pre-pulsecurrent from the current that is obtained after the pulse is switchedoff, plotted against the applied potential. The correspondingsensitivity is thereby increased. The differential pulse voltammetrytechniques vary by the shape of the applied potential waveform, and thecurrent sampling technique.

Alongside increased sensitivity, differential pulse voltammetry allowsthe detection of two different analytes with similar redox potentials,by analysis of the peak's width according to the number of electronsthat participate in their redox reaction. Exemplary values used fordifferential voltammetry measurements are 25-50 mV for current pulseamplitudes and 5 mV/second for the scan rate, while steeper amplitudesand faster scan rates are also contemplated.

In some of any of the embodiments described herein, the potential is alinearily varying potential.

In some of any of the embodiments described herein, the potential is adifferential pulse varying potential.

In some of any of the embodiments described herein, the range of avarying potential ranges from −2 to +1 Volts, including any intermediatesubranges therebetween.

In some of any of the embodiments described herein, an electrochemicalparameter measured in a method as described herein is a change inelectrical current relative to a derivative of the applied potential,although any other voltammogram is contemplated.

In some of any of the embodiments described herein, the measuredelectrochemical parameter is processed by a signal processor, asdescribed herein in any of the respective embodiments, to therebydetermine a presence, a composition and/or a level of one or morenitro-containing compounds in the sample.

In some of any of the embodiments described herein, a time ranging fromintroducing a sample so as to contact the sensing electrode to measuringthe electrochemical parameter is less than 2 minutes, or less than 1minute, or even less than 30 seconds, or less than 20 seconds, or less.

In some of any of the embodiments described herein, the method furthercomprises, prior to contacting the sample with the sensing electrode(e.g., prior to introducing the sample to the electrochemical cell),applying the potential, and measuring the electrochemical parameter, tothereby measure a background signal. In some embodiments, upon measuringthe electrochemical parameter resulting from contacting the sensingsystem and the sample, the background signal is subtracted from themeasured electrochemical parameter.

In some of any of the embodiments described herein, the method furthercomprises, prior to contacting the sample with the sensing electrode(e.g., prior to introducing the sample to the electrochemical cell),repetitively applying a potential, for at least 2 consecutive cycles. Insome embodiments, the potential is applied from 2 to 20, or from 5 to20, or from 5 to 15, or for 10, cycles, prior to contacting the samplewith the sensing electrode.

In some embodiments, repetitively applying the potential is performed(the number of consecutive cycles is selected) prior to contacting thesample such that up to 70 mol %, or up to 65 mol % of the total numberof moles of metal species is in a form of metal particles, as describedherein in any of the respective embodiments.

In some embodiments, repetitively applying the potential is performed(the number of consecutive cycles is selected), prior to contacting thesample, such that up to 50 mol %, or up to 40 mol % of the total numberof moles of metal species originally deposited on the electrode'ssurface (before applying the potential) is transformed (converted) tometal particles, as described herein in any of the respectiveembodiments.

In some embodiments, repetitively applying the potential is performed(the number of consecutive cycles is selected), prior to contacting thesample, such that the functional moiety comprises ions of a metal andparticles of the same metal (in elemental form), and such that a molratio of the metal ions and the metal particles ranges from 75:25 to25:75, or from 70:30 to 30:70, as described herein in any of therespective embodiments.

In some embodiments, repetitively applying the potential is performed(the number of consecutive cycles is selected), prior to contacting thesample, such that the functional moiety comprises particles of a metaland ions of the same metal, and oxide of the same metal, and a mol ratioof the ions of the metal and the particles of the metal, or of the ionsof the metal and the total amount of metal particles (e.g., particles ofelemental metal and of the metal oxide), or of the metal ions and themetal oxide or of the elemental metal and the metal oxide are asdescribed herein in any of the respective embodiments.

In some embodiments, repetitively applying the potential is performed(the number of consecutive cycles is selected), prior to contacting thesample, such that the functional moiety comprises particles of a metaland ions of the same metal, and oxide of the same metal, each in anamount as described herein in any of the respective embodiments.

In some of any of the embodiments described herein, the method furthercomprises, subsequent to measuring the electrochemical parameter,applying an opposite potential to the sensing electrode, to therebyregenerate the electrode.

In some of any of the embodiments described herein, a method asdescribed herein is effected in an oxygen-containing environment, asdescribed herein.

Sample:

A peroxide-containing compound is used herein to describe organic andinorganic compounds that include one or more peroxides [—O—O—]. Thecompound can be comprised of an aliphatic or alicyclic or aromatichydrocarbon moiety, substituted by one or more peroxide-containinggroups such as, for example, O—OR groups, with R being alkyl,cycloalkyl, aryl, hydrogen and the like. The hydrocarbon moiety canoptionally be interrupted by one or more heteroatoms, such as nitrogen,oxygen, sulfur, phosphor, silicon, boron. The hydrocarbon moiety canoptionally be further substituted by other substituents, as describedherein. Alternatively, or in addition, the compound can be comprised ofa hydrocarbon (e.g., aliphatic or alicyclic) interrupted by one orperoxide groups.

Peroxide-containing explosives are typically cyclic compounds, whichinclude one or more peroxides interrupting the cyclic hydrocarbon, andmay optionally be substituted and/or include additional interruptingheteroatoms. Examples include, but are not limited to, TATP, HMDT andTMDD.

Linear peroxide-containing explosives are also contemplated, as well asinorganic peroxide-containing compounds or compounds capable ofgenerating peroxide-containing compounds.

Herein, the term “peroxide-containing compound” or “peroxide-containingmaterial” does not encompass hydrogen peroxide.

For any one of the embodiments described herein, the sample encompassessamples suspected as containing a peroxide-containing compound, suchthat the systems and methods described herein are utilized fordetermining a presence and optionally an amount of a peroxide-containingcompound and further optionally an identity (e.g., the chemicalcomposition) of a peroxide-containing compound.

Optionally, the sample is known to contain a peroxide-containingcompound and the methods and systems described herein are utilized fordetermining an amount and/or identity of the peroxide-containingcompound in the sample.

For any of the embodiments described herein, the methods and systemsdescribed herein can be used for identifying a presence or absence of aperoxide-containing compound as described herein, and can be efficientlyutilized for discriminating a peroxide-containing compound (e.g.,peroxide-containing explosives) from chemically-related compounds ormixtures of compounds (e.g., hydrogen peroxide).

For example, when a sample is suspected as containing aperoxide-containing compound which is an explosive, the methods andsystems described herein can be used to determine if the compound is aperoxide-containing compound or a chemically-related non-explosivecompound such as hydrogen peroxide.

As used herein, the term “explosive” encompasses an explosive material,an explosive residue (e.g., a substance obtained upon explosion) and amaterial associated with an explosive material (e.g., a startingmaterial for preparing an explosive material).

Herein, a peroxide-containing compound is also referred tointerchangeably as an analyte.

In some of any of the embodiments described herein, the sample is afluid sample, and can be a liquid sample or a gaseous sample.

In some of any of the embodiments described herein, the sample is air.

In some of any of the embodiments described herein, theperoxide-containing compound is in a fluid state (e.g., is in a liquidstate or a gaseous state).

The term “fluid” is defined as a substance that tends to flow and toconform to the outline of its container. Typical fluids include liquidsand gasses, but may also include free flowing solid particles.

In some of any of the embodiments described herein, theperoxide-containing compound is in a gaseous state.

By “gaseous state” it is meant that at least a portion of the compoundis in a form of vapors. Thus, for example, the compound can be a liquidor a solid at room temperature, yet, it is volatile to some extent, suchthat a portion thereof is in a gaseous state at room temperature.Alternatively, the compound can be in such a gaseous state upon heatinga sample containing same.

Since, as noted herein, the method and system described herein can beutilized for detecting ultra-trace amounts of peroxide-containingcompounds, the portion of a compound in a gaseous state can beultra-law, as is further detailed hereinbelow.

In some of any of the embodiments described herein, a concentration ofthe peroxide-containing compound in the sample is lower than 1micromolar.

The concentration of the peroxide-containing compound encompasses aconcentration of the compound's vapors in air or other gaseous samples,as well as a concentration of the compound in a liquid sample.

Accordingly, in some of any of the embodiments described herein, themethod and system described herein can be utilized to detectlow-volatile peroxide-containing compounds, without concentrating thesample and/or heating the sample prior to contacting it with the system.

Since, as noted herein, the method and system described herein can beutilized for detecting ultra-trace amounts of peroxide-containingcompounds, the portion of a compound in a gaseous state can beultra-law, as is further detailed hereinbelow.

In some of any of the embodiments described herein, a concentration ofthe peroxide-containing compound in the sample is lower than 1micromolar.

The concentration of the peroxide-containing compound encompasses aconcentration of the compound's vapors in air or other gaseous samples,as well as a concentration of the compound in a liquid sample.

Accordingly, in some of any of the embodiments described herein, themethod and system described herein can be utilized to detectlow-volatile peroxide-containing compounds, with ultra-low vaporpressure, without concentrating the sample and/or heating the sampleprior to contacting it with the system.

In some of any of the embodiments described herein, the sample comprisestwo or more peroxide-containing compounds.

In some of any of the embodiments described herein, a sample comprisesone or more peroxide-containing compounds, and one or more additionalcompounds of interest (target compounds or analytes).

In some of any of the embodiments described herein, the sample comprisesoxygen.

If the sample is a gaseous sample (e.g. air), the sample inherentlycomprises oxygen, and when it is dissolved in an electrolyte, dissolvedoxygen is also present in the electrolyte.

If the sample is a liquid sample, for example sea water or from anyother water source, it also comprises dissolved oxygen.

A sample as described herein can be analyzed using the methods andsystems as described herein per se, without further processing.

It is expected that during the life of a patent maturing from thisapplication many relevant electrodes and electrochemical cellconfigurations will be developed and the scope of the term electrode andelectrochemical cell is intended to include all such new technologies apriori.

As used herein the term “about” refers to ±10% or ±5%.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

As used herein, the singular form “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a compound” or “at least one compound” may include a pluralityof compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention maybe presented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, the description of a range should be consideredto have specifically disclosed all the possible subranges as well asindividual numerical values within that range. For example, descriptionof a range such as from 1 to 6 should be considered to have specificallydisclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numberswithin that range, for example, 1, 2, 3, 4, 5, and 6. This appliesregardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to includeany cited numeral (fractional or integral) within the indicated range.The phrases “ranging/ranges between” a first indicate number and asecond indicate number and “ranging/ranges from” a first indicate number“to” a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numerals therebetween.

As used herein the term “method” refers to manners, means, techniquesand procedures for accomplishing a given task including, but not limitedto, those manners, means, techniques and procedures either known to, orreadily developed from known manners, means, techniques and proceduresby practitioners of the chemical, pharmacological, biological,biochemical and medical arts.

As used herein, the term “amine” describes both a —NR′R″ group and a—NR′— group, wherein R′ and R″ are each independently hydrogen, alkyl,cycloalkyl, aryl, as these terms are defined hereinbelow.

The amine group can therefore be a primary amine, where both R′ and R″are hydrogen, a secondary amine, where R′ is hydrogen and R″ is alkyl,cycloalkyl or aryl, or a tertiary amine, where each of R′ and R″ isindependently alkyl, cycloalkyl or aryl.

Alternatively, R′ and R″ can each independently be hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, carbonyl, C-carboxylate, O-carboxylate,N-thiocarbamate, O-thiocarbamate, urea, thiourea, N-carbamate,O-carbamate, C-amide, N-amide, guanyl, guanidine and hydrazine.

The term “amine” is used herein to describe a —NR′R″ group in caseswhere the amine is an end group, as defined hereinunder, and is usedherein to describe a —NR′— group in cases where the amine is a linkinggroup.

Herein throughout, the phrase “end group” describes a group (asubstituent) that is attached to another moiety in the compound via oneatom thereof.

The phrase “linking group” describes a group (a substituent) that isattached to another moiety in the compound via two or more atomsthereof.

The term “alkyl” describes a saturated aliphatic hydrocarbon includingstraight chain and branched chain groups. Preferably, the alkyl grouphas 1 to 20 carbon atoms. Whenever a numerical range; e.g., “1-20”, isstated herein, it implies that the group, in this case the alkyl group,may contain 1 carbon atom, 2 carbon atoms, 3 carbon atoms, etc., up toand including 20 carbon atoms. More preferably, the alkyl is a mediumsize alkyl having 1 to 10 carbon atoms. Most preferably, unlessotherwise indicated, the alkyl is a lower alkyl having 1 to 5 carbonatoms. The alkyl group may be substituted or unsubstituted. Substitutedalkyl may have one or more substituents, whereby each substituent groupcan independently be, for example, hydroxyalkyl, trihaloalkyl,cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl, heteroalicyclic, amine,halide, sulfonate, sulfoxide, phosphonate, hydroxy, alkoxy, aryloxy,thiohydroxy, thioalkoxy, thioaryloxy, cyano, nitro, azo, sulfonamide,C-carboxylate, O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea,thiourea, N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidineand hydrazine.

The alkyl group can be an end group, as this phrase is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this phrase is defined hereinabove, which connects twoor more moieties via at least two carbons in its chain.

The term “aminoalkyl” is used herein to describe an alkyl substituted byan amine, as defined herein. In some embodiments, the amine substitutesa terminal carbon atom in the alkyl.

The term “cycloalkyl” describes an all-carbon monocyclic or fused ring(i.e., rings which share an adjacent pair of carbon atoms) group whereone or more of the rings does not have a completely conjugatedpi-electron system. The cycloalkyl group may be substituted orunsubstituted. Substituted cycloalkyl may have one or more substituents,whereby each substituent group can independently be, for example,hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl,heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The cycloalkyl group can be an end group, as this phrase isdefined hereinabove, wherein it is attached to a single adjacent atom,or a linking group, as this phrase is defined hereinabove, connectingtwo or more moieties at two or more positions thereof.

The term “aryl” describes an all-carbon monocyclic or fused-ringpolycyclic (i.e., rings which share adjacent pairs of carbon atoms)groups having a completely conjugated pi-electron system. The aryl groupmay be substituted or unsubstituted. Substituted aryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,N-carbamate, O-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The aryl group can be an end group, as this term is definedhereinabove, wherein it is attached to a single adjacent atom, or alinking group, as this term is defined hereinabove, connecting two ormore moieties at two or more positions thereof.

The term “heteroaryl” describes a monocyclic or fused ring (i.e., ringswhich share an adjacent pair of atoms) group having in the ring(s) oneor more atoms, such as, for example, nitrogen, oxygen and sulfur and, inaddition, having a completely conjugated pi-electron system. Examples,without limitation, of heteroaryl groups include pyrrole, furane,thiophene, imidazole, oxazole, thiazole, pyrazole, pyridine, pyrimidine,quinoline, isoquinoline and purine. The heteroaryl group may besubstituted or unsubstituted. Substituted heteroaryl may have one ormore substituents, whereby each substituent group can independently be,for example, hydroxyalkyl, trihaloalkyl, cycloalkyl, alkenyl, alkynyl,aryl, heteroaryl, heteroalicyclic, amine, halide, sulfonate, sulfoxide,phosphonate, hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy,thioaryloxy, cyano, nitro, azo, sulfonamide, C-carboxylate,O-carboxylate, N-thiocarbamate, O-thiocarbamate, urea, thiourea,O-carbamate, N-carbamate, C-amide, N-amide, guanyl, guanidine andhydrazine. The heteroaryl group can be an end group, as this phrase isdefined hereinabove, where it is attached to a single adjacent atom, ora linking group, as this phrase is defined hereinabove, connecting twoor more moieties at two or more positions thereof. Representativeexamples are pyridine, pyrrole, oxazole, indole, purine and the like.

The term “heteroalicyclic” describes a monocyclic or fused ring grouphaving in the ring(s) one or more atoms such as nitrogen, oxygen andsulfur. The rings may also have one or more double bonds. However, therings do not have a completely conjugated pi-electron system. Theheteroalicyclic may be substituted or unsubstituted. Substitutedheteroalicyclic may have one or more substituents, whereby eachsubstituent group can independently be, for example, hydroxyalkyl,trihaloalkyl, cycloalkyl, alkenyl, alkynyl, aryl, heteroaryl,heteroalicyclic, amine, halide, sulfonate, sulfoxide, phosphonate,hydroxy, alkoxy, aryloxy, thiohydroxy, thioalkoxy, thioaryloxy, cyano,nitro, azo, sulfonamide, C-carboxylate, O-carboxylate, N-thiocarbamate,O-thiocarbamate, urea, thiourea, O-carbamate, N-carbamate, C-amide,N-amide, guanyl, guanidine and hydrazine. The heteroalicyclic group canbe an end group, as this phrase is defined hereinabove, where it isattached to a single adjacent atom, or a linking group, as this phraseis defined hereinabove, connecting two or more moieties at two or morepositions thereof. Representative examples are piperidine, piperazine,tetrahydrofurane, tetrahydropyrane, morpholino and the like.

The term “amine-oxide” describes a —N(OR′)(R″) or a —N(OR′)— group,where R′ and R″ are as defined herein. This term refers to a —N(OR′)(R″)group in cases where the amine-oxide is an end group, as this phrase isdefined hereinabove, and to a —N(OR′)— group in cases where theamine-oxime is an end group, as this phrase is defined hereinabove.

The term “halide” and “halo” describes fluorine, chlorine, bromine oriodine.

The term “haloalkyl” describes an alkyl group as defined above, furthersubstituted by one or more halide.

The term “sulfate” describes a —O—S(═O)₂—OR′ end group, as this term isdefined hereinabove, or an —O—S(═O)₂—O— linking group, as these phrasesare defined hereinabove, where R′ is as defined hereinabove.

The term “thiosulfate” describes a —O—S(═S)(═O)—OR′ end group or a—O—S(═S)(═O)—O— linking group, as these phrases are defined hereinabove,where R′ is as defined hereinabove.

The term “sulfite” describes an —O—S(═O)—O—R′ end group or a —O—S(═O)—O—group linking group, as these phrases are defined hereinabove, where R′is as defined hereinabove.

The term “thiosulfite” describes a —O—S(═S)—O—R′ end group or an—O—S(═S)—O— group linking group, as these phrases are definedhereinabove, where R′ is as defined hereinabove.

The term “sulfinate” describes a —S(═O)—OR′ end group or an —S(═O)—O—group linking group, as these phrases are defined hereinabove, where R′is as defined hereinabove.

The term “sulfoxide” or “sulfinyl” describes a —S(═O)R′ end group or an—S(═O)— linking group, as these phrases are defined hereinabove, whereR′ is as defined hereinabove.

The term “sulfonate” describes a —S(═O)₂—R′ end group or an —S(═O)₂—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “S-sulfonamide” describes a —S(═O)₂—NR′R″ end group or a—S(═O)₂—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-sulfonamide” describes an R'S(═O)₂—NR″— end group or a—S(═O)₂—NR′— linking group, as these phrases are defined hereinabove,where R′ and R″ are as defined herein.

The term “disulfide” refers to a —S—SR′ end group or a —S—S— linkinggroup, as these phrases are defined hereinabove, where R′ is as definedherein.

The term “carbonyl” or “carbonate” as used herein, describes a —C(═O)—R′end group or a —C(═O)— linking group, as these phrases are definedhereinabove, with R′ as defined herein.

The term “thiocarbonyl” as used herein, describes a —C(═S)—R′ end groupor a —C(═S)— linking group, as these phrases are defined hereinabove,with R′ as defined herein.

The term “oxime” describes a ═N—OH end group or a ═N—O— linking group,as these phrases are defined hereinabove.

The term “hydroxyl” describes a —OH group.

The term “alkoxy” describes both an —O-alkyl and an —O-cycloalkyl group,as defined herein.

The term “aryloxy” describes both an —O-aryl and an —O-heteroaryl group,as defined herein.

The term “thiohydroxy” describes a —SH group.

The term “thioalkoxy” describes both a —S-alkyl group, and a—S-cycloalkyl group, as defined herein.

The term “thioaryloxy” describes both a —S-aryl and a —S-heteroarylgroup, as defined herein.

The term “cyano” describes a —C≡N group.

The term “isocyanate” describes an —N═C═O group.

The term “nitro” describes an —NO₂ group.

The term “acyl halide” describes a —(C═O)R″″ group wherein R″″ ishalide, as defined hereinabove.

The term “azo” or “diazo” describes an —N═NR′ end group or an —N═N—linking group, as these phrases are defined hereinabove, with R′ asdefined hereinabove.

The term “C-carboxylate” describes a —C(═O)—OR′ end group or a —C(═O)—O—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “O-carboxylate” describes a —OC(═O)R′ end group or a —OC(═O)—linking group, as these phrases are defined hereinabove, where R′ is asdefined herein.

The term “C-thiocarboxylate” describes a —C(═S)—OR′ end group or a—C(═S)—O— linking group, as these phrases are defined hereinabove, whereR′ is as defined herein.

The term “O-thiocarboxylate” describes a —OC(═S)R′ end group or a—OC(═S)— linking group, as these phrases are defined hereinabove, whereR′ is as defined herein.

The term “N-carbamate” describes an R″OC(═O)—NR′— end group or a—OC(═O)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “O-carbamate” describes an —OC(═O)—NR′R″ end group or an—OC(═O)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “O-thiocarbamate” describes a —OC(═S)—NR′R″ end group or a—OC(═S)—NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-thiocarbamate” describes an R″OC(═S)NR′— end group or a—OC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “S-dithiocarbamate” describes a —SC(═S)—NR′R″ end group or a—SC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “N-dithiocarbamate” describes an R″SC(═S)NR′— end group or a—SC(═S)NR′— linking group, as these phrases are defined hereinabove,with R′ and R″ as defined herein.

The term “urea”, which is also referred to herein as “ureido”, describesa —NR′C(═O)—NR″R′″ end group or a —NR′C(═O)—NR″— linking group, as thesephrases are defined hereinabove, where R′ and R″ are as defined hereinand R′″ is as defined herein for R′ and R″.

The term “thiourea”, which is also referred to herein as “thioureido”,describes a —NR′—C(═S)—NR″R′″ end group or a —NR′—C(═S)—NR″— linkinggroup, with R′, R″ and R′″ as defined herein.

The term “C-amide” describes a —C(═O)—NR′R″ end group or a —C(═O)—NR′—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “N-amide” describes a R′C(═O)—NR″— end group or a R′C(═O)—N—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “guanyl” describes a R′R″NC(═N)— end group or a —R′NC(═N)—linking group, as these phrases are defined hereinabove, where R′ and R″are as defined herein.

The term “guanidine” describes a —R′NC(═N)—NR″R′″ end group or a—R′NC(═N)— NR″— linking group, as these phrases are defined hereinabove,where R′, R″ and R′″ are as defined herein.

The term “hydrazine” describes a —NR′—NR″R′″ end group or a —NR′—NR″—linking group, as these phrases are defined hereinabove, with R′, R″,and R′″ as defined herein.

The term “silyl” describes a —SiR′R″R′″ end group or a —SiR′R″— linkinggroup, as these phrases are defined hereinabove, whereby each of R′, R″and R′″ are as defined herein.

The term “siloxy” describes a —Si(OR′)R″R′″ end group or a—Si(OR′)R″-linking group, as these phrases are defined hereinabove,whereby each of R′, R″ and R′″ are as defined herein.

The term “silaza” describes a —Si(NR′R″)R′″ end group or a —Si(NR′R″)—linking group, as these phrases are defined hereinabove, whereby each ofR′, R″ and R′″ is as defined herein.

The term “silicate” describes a —O—Si(OR′)(OR″)(OR′″) end group or a—O—Si(OR′)(OR″)— linking group, as these phrases are definedhereinabove, with R′, R″ and R′″ as defined herein.

As used herein, the term “hydrazide” describes a —C(═O)—NR′—NR″R′″ endgroup or a —C(═O)—NR′—NR″— linking group, as these phrases are definedhereinabove, where R′, R″ and R′″ are as defined herein.

As used herein, the term “thiohydrazide” describes a —C(═S)—NR′—NR″R′″end group or a —C(═S)—NR′—NR″— linking group, as these phrases aredefined hereinabove, where R′, R″ and R′″ are as defined herein.

As used herein, the term “methyleneamine” describes an—NR′—CH₂—CH═CR″R′″ end group or a —NR′—CH₂—CH═CR″— linking group, asthese phrases are defined hereinabove, where R′, R″ and R′″ are asdefined herein.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Various embodiments and aspects of the present invention as delineatedhereinabove and as claimed in the claims section below find experimentalsupport in the following examples.

EXAMPLES

Reference is now made to the following examples, which together with theabove descriptions illustrate some embodiments of the invention in a nonlimiting fashion.

Materials and Methods

Spectracarb™ 2050A-1050 carbon paper microelectrode, 0.18 mm thick wasobtained from Engineered Fiber Technology, USA. Electrode samples havingan area of 0.35 cm² were used in all experiments, unless otherwiseindicated.

Nickel foil (thickness of 0.125 mm, ≥99.9%), Tetrabutylammonium iodide(TBA-I≥98.0%, electrochemical grade), Acetonitrile (99.8%), and Ethanol(≥99.5%), were purchased from Sigma-Aldrich, Israel.

Silver benzoate (99%) was obtained from Sigma-Aldrich, Israel

Nafion® 117 solution was obtained from Sigma-Aldrich, Israel.

Hexamethylenetetramine (99+%), tetra-n-butylammoniumtetrafluoroborate(TBABF₄, 99+%, electrochemical grade), hydrogen peroxide (30%),anhydrous citric acid (99.5+%), sulfuric acid (95-98%), silver benzoate(99%), acetone (99.8+%), acetonitrile (99.8%), N, N-dimethylformamide(99.8%), ethanol (99.5+%), and 1, 2-dichloroethane (99.8%) werepurchased from Sigma-Aldrich, Israel.

Triacetonetriperoxide (TATP) was synthesized by a reaction of acetonewith 30% H₂O₂ in the presence of sulfuric acid at −20° C., as describedin Oxley et al. Propell Explos Pyrot 27, 209-216, 2002.

Hexamethylenetriperoxide diamine (HMTD) was obtained by the reaction ofhexamethylenetetramine with 30% H₂O₂ in the presence of anhydrous citricacid at 0° C.

Parafilm PM996 was purchased from Alex Red, Israel.

All other reagents were obtained from known vendors.

Millipore Mill-Q water (deionized water, 18 mega-ohm) was used in allexperiments.

Scanning electron microscope (SEM) measurements were performed usingQuanta 200 FEG environmental scanning electron microscope.

X-ray Photoelectron Spectroscopy (XPS) measurements were performed inUHV (2.5×10⁻¹⁰ Torr base pressure) using 5600 Multi-Technique System(PHI, USA). The sample was irradiated with an Al K_(α) monochromatedsource (1486.6 eV) and the outcome electrons were analyzed by aSpherical Capacitor Analyzer using the slit aperture of 0.8 mm. Thesamples were analyzed at the surface only. They were uncharged duringmeasurements.

A three-electrode electrochemical cell (volume 3 ml) was used in allexperiments, unless otherwise indicated, in which a glassy carbonelectrode was used as the counter electrode, a silver-silver chloride(Ag—AgCl), with 3 molar potassium chloride, was used as the referenceelectrode with a double junction salt bridge (Metrohm), andmicro-carbon-fibers (0.35 cm², 0.18 mm in diameter), ormicro-carbon-fibers chemical modified electrode (0.35 cm², 0.18 mm indiameter) was used as the working electrode.

A non-modified working electrode was prepared from micro-carbon-fiberspaper (0.18×20×5 mm), and nickel foil (0.2×25×5 mm) as a currentcollector (electrical contact); the connection and the insulation ofmicro-carbon-fibers with nickel contact was performed by Parafilm. Theelectrode with current collector was pressed with a pressure of about 2kg/cm² for 30 seconds at room temperature. The electrode was carefullywashed with ethanol, rinsed with distilled water and dried at roomtemperature.

Linear sweep and cyclic voltammetries were performed using AutolabPGSTAT 302N. The scan rate of performed linear sweep voltammetryregistration was 0.1 volt/second.

Example 1 TATP and H₂O₂ Reduction Peaks Obtained by Unmodified CFMicroelectrode

As background reference experiments, the electrochemical detection ofperoxide-based explosives in the presence of H₂O₂ and dissolved oxygenwas performed using unmodified carbon fiber (CF) microelectrode having asurface area of 0.35 cm². A high-pH electrolyte solution was selected,assuming it may influence the stability of the H₂O₂ and decrease thereduction potential of H₂O₂ compared to peroxide based explosives. Theselected solution contained a mixture of NaOH in deionized water (pH=12)and acetonitrile at 7:3 volume ratio and 0.1 M TBABF₄.

Linear sweep voltammetry registration was performed at a scan rate of0.1 volt/second.

The obtained data is presented in FIG. 1. The black line represents thebackground without TATP addition, the red, blue and turquoise linesrepresent the background with 20, 40 and 60 ppm of TATP additionrespectively, and the pink line represents the background with 60 ppmTATP and 40 ppm H₂O₂.

As shown in FIG. 1, the high pH conditions did not result in separationof the two reduction peaks, and the reduction potentials of both H₂O₂and TATP on the unmodified electrode were both around 1.35 volt.

Example 2 HMTD and H₂O₂ Reduction Peaks Obtained by SilverBenzoate-Modified CF Microelectrode

The present inventors have conceived utilizing the catalytic activity ofsilver in H₂O₂ decomposition reaction for promoting the separation ofH₂O₂ and peroxide-based explosives current peaks. To this effect, thepresent inventors have sought for a stable silver modification of the CFmicroelectrode, and have used silver benzoate and Nafion® modification.

A modification of a CF microelectrode with silver benzoate was carriedout by tipping 15 μl of 1% silver benzoate and 1% Nafion® 117 in ethanolon the electrode and air-drying or N₂-drying at 40° C. for 60 minutes.Due to the organometallic properties of silver benzoate, the silverefficiently absorbed to the carbon microfibers.

The Nafion® serves as coating exchange membrane that prevents thewashing of silver benzoate from the working electrode surface.

Linear sweep voltammetry registration was performed at a scan rate of0.1 volt/second, while using a high pH electrolyte solution as describedin Example 1 herein.

The obtained data is presented in FIGS. 2A-2C.

In FIG. 2A, the black line represents the background without HMDTaddition, and the other lines represent the background with addition ofHMDT at the indicated concentrations.

As shown in FIG. 2A, efficient separation of the H₂O₂ current peak,appearing at −0.4 Volts) from that of HMTD, appearing between −0.8 to−0.9 Volts, was obtained. A drift of the HMTD's current peak towards thenegative spectrum of voltages in a concentration dependant manner wasobserved, indicating some instability of the modification.

FIG. 2B presents a calibration curve based on current peaks of HMTD asmarked by a green arrow. ΔI=background current−current peak of HMTD. Itcan be seen that the detection of HMTD was performed in highconcentration dependence (R=0.993).

FIG. 2C presents the data obtained upon addition of 180 ppm HMTD (blackline) of 180 ppm HMTD and 40 ppm H₂O₂(red line).

Example 3 Scanning Electron Microscope and X-Ray PhotoelectronSpectroscopy Analyses of Silver Benzoate Modified CF Microelectrode

The CF microelectrode surface was analyzed by scanning electronmicroscope (SEM) using secondary electrons (SE) and backscatteredelectrons (BSE). Then atomic concentrations of carbon (C), oxygen (O),silver (Ag), fluorine (F), sulfur (S), were determined using X-rayphotoelectron spectroscopy atomic (XPS) concentrations. The surfaceanalyses of the unmodified CF microelectrode are presented in FIG. 3A.The surface analyses of the silver benzoate-modified CF microelectrodeafter performing one linear sweep voltammetry scans from 0 volts to −1.6volts, at a scan rate of 0.1 volt/second in the electrolyte solution asdescribed in Example 1 herein are presented in FIG. 3B. The surfaceanalyses of the modified CF microelectrode after performing 100 linearsweep voltammetry scans from 0 volts to −1.6 volts, at a scan rate of0.1 volt/second in the electrolyte solution as described in Example 1herein is presented in FIG. 3C.

The unmodified CF microelectrode was first analyzed using scanningelectron microscope (SEM) by secondary electrons (SE) and backscatteredelectrons (BSE). The obtained data is presented in FIG. 3A (rightpanel), and show that the CF microelectrode is composed of rough fiberswith few microns width, which contributed to the active surface area ofthe electrode.

After the modification with silver benzoate and use in one linear sweepvoltammetry scan of from 0 volts to −1.6 volts, with addition of TATP tothe electrolyte, the SEM-SE and SEM-BSE images, presented in FIG. 3B,right panel, show a formation of silver nano-particles distributed inlow density around the carbon fibers surface.

After the modified micro-carbon-fibers electrode was used for 100repetitions of the same electrochemical measurement, the SEM-SE andSEM-BSE, presented in FIG. 3B, right panel, showed an increased amountand distribution of the silver nano-particles around the carbon fiberssurface.

These findings suggest that the voltage applied to the surface of theelectrode leads to reduction of the silver benzoate and formation ofsilver nanoparticles, which changes the surface area and the chemicalproperties of the electrode.

The reduction of silver benzoate as a result of the electrochemicalmeasurement is shown in the X-ray photoelectron spectroscopy (XPS) dataobtained. The XPS analysis shows a decrease in the atomic concentrationof organometallic (Organo Ag) and silver oxide (Oxide Ag) on the surfaceof the modified CF microelectrode after 100 repetitions ofelectrochemical measurements of linear sweep voltammetry scan from 0volts to −1.6 volts (see, FIG. 3C, left panel). The atomic concentrationof metallic silver (Metallic Ag) increased as a result of the performed100 electrochemical measurements (see, FIG. 3C, left panel).

The presence of fluorine (F) and sulfur (S) indicated a successfulmodification by Nafion on the electrode surface. See, FIGS. 3B and 3C,left panels.

X-ray crystallography (RXD) analysis showed that the average size of theformed silver nano-particles as a result of the electrochemicalmeasurement was about 40 nm (data not shown).

Example 4 Detection of TATP and HMTD in the Presence of Dissolved Oxygenand H₂O₂

In an attempt to stabilize the silver benzoate modification and obtainreproducible current peaks of peroxide-based explosives, the linearsweep voltammetry scans from 0 volts to −1.6 volts were performed in theelectrolyte solution 10-15 subsequent times prior to the detection ofperoxide based explosives.

The data obtained upon addition of HMTD, following 15 subsequentrepetitions of the linear sweep voltammetry scans is presented in FIGS.4A-4C. The data obtained upon addition of TAPT, following 15 subsequentrepetitions of the linear sweep voltammetry scans is presented in FIGS.5A-5C.

In FIGS. 4A and 5A, the black line represents data obtained for thebackground electrolyte without HMDT or TAPT addition, and the otherlines represent the data obtained upon addition of HMDT or TAPT at theindicated concentrations.

As shown in FIGS. 4A and 5A, efficient separation of the H₂O₂ currentpeak, appearing at about −0.5 Volts, from that of HMTD, appearing atabout −1.5 Volts, and of TAPT, appearing at about −1.4 Volts, wasobtained. Importantly, no drift of the current peaks was observed. TheH₂O₂ current peak barely affected the current peaks of HMTD and TATP.

The green arrow in FIGS. 4A and 5A represents the current peaks thatwere used for the calibration curve presented in FIGS. 4B and 5B,respectively. ΔI=background current−current peak of HMTD.

It can be seen that the detection of both peroxide-based explosives wasperformed in high concentration dependence (R=0.997), and could bedistinguished by a characteristic shape of the peak FIG. 4C presents thedata obtained upon addition of 150 ppm HMTD (black line) and of 150 ppmHMTD and 40 ppm H₂O₂(red line).

FIG. 5C presents the data obtained upon addition of 180 ppm TATP (blackline) and of 150 ppm TATP and 30 ppm H₂O₂(red line).

The analysis of a single sample took 16 seconds, hence meets the need offield condition sensing of explosive.

These data indicate that utilization of stabilized silver nanoparticlesmicro-carbon-fibers electrode is an efficient method for the detectionof peroxide-based explosives, in the presence of H₂O₂ and dissolvedoxygen. The catalytic capabilities of this modification route enabled toperform current peak separation of peroxide-based explosives from H₂O₂and O₂ peaks in a single measurement cycle of linear sweep voltammetry,without using time-consuming pre-processing steps. The whole measurementlasts approximately 10 seconds. The shape of the current peak and itsvoltage could be used to distinguish between different peroxide-basedexplosives, and thereby add multiplex capabilities to the detectionmethod. A detection limit of the peroxide-based explosives using linearsweep voltammetry can be around 0.25 ppm. In order to further improvethe detection limit a differential pulse voltammetry can be applied.

Thus, silver nanoparticles chemical modification of micro-carbon-fiberselectrodes enabled to perform real-time, label-free, low cost, robust,selective and sensitive direct detection of peroxide-based explosives,such as TATP and HMTD, in sub-ppm level concentrations without applyingpre-processing steps, thereby combining simplicity and rapid samplingrate.

Example 5 Gas Phase Detection of TATP

EmStat system was used for voltammetry registration in the linear sweepregimes. The scan rate of performed linear sweep voltammetryregistration was 0.1 volt/second.

A conventional three-electrode cell (volume 3 ml), in which a glassycarbon electrode was used as the counter electrode, a silver-silverchloride (Ag—AgCl), with 3 molar potassium chloride, was used as thereference electrode with a double junction salt bridge (Metrohm), and amicro-carbon-fibers (0.35 cm², 0.18 mm thickness), ormicro-carbon-fibers chemically modified electrode (0.35 cm², 0.18 mmthickness) was used as the working electrode. The background solutioncontained a mixture of sodium hydroxide in deionized water (pH=12), andacetonitrile at 7:3 volume ratio, 0.1 Mtetra-n-butylammoniumtetrafluoroborate.

A modification of micro-carbon-fibers electrode with silver benzoate wascarried out by dropping 15 μl of 1% silver benzoate and 1% Nafion® 117in ethanol on the electrode surface and air-drying at 40° C. for 60minutes.

TATP (prepared as described herein) was absorbed to a filter paper as asolution of 10 mg in ethanol. The soaked paper was placed in a closedbox for about an hour prior to measurements to achieve TATP vaporsaturation.

The vapors were then pumped by means of an air pump, through a tube thatconnected the TATP vapors, the tested electrode and the pump (in aconfiguration in which the vapors contact the electrode while beingpumped).

The obtained data is presented in FIG. 7 and clearly show the detectionof distinct signal.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting. In addition, any priority document(s) of this applicationis/are hereby incorporated herein by reference in its/their entirety.

What is claimed is:
 1. A sensing electrode comprising a carbon electrodeand a functional moiety being in association with at least a portion ofa surface of said electrode, said functional moiety comprising at leastone metal species that promotes decomposition of hydrogen peroxide. 2.The electrode of claim 1, wherein said electrode is a carbon fibermicroelectrode.
 3. The electrode of claim 1, wherein said carbonelectrode is gas-permeable.
 4. The electrode of claim 1, wherein saidfunctional moiety comprises metal ions.
 5. The electrode of claim 4,wherein said metal ions undergo reduction to thereby provide metalparticles, upon application of a potential in a range of from about−0.05 to about 2 volts.
 6. The electrode of claim 4, wherein saidfunctional moiety further comprises particles of said metal.
 7. Theelectrode of claim 6, wherein an amount of said particles of said metalis less than 70 mol %, or less than 65 mol %, of the total number ofmoles of said metal in said functional moiety.
 8. The electrode of claim6, wherein a mol ratio of said metal ions and said particles of saidmetal ranges from 70:30 to 30:70.
 9. The electrode of claim 1, whereinsaid metal is silver.
 10. The electrode of claim 1, wherein saidfunctional moiety comprises at least one metal species having an organicmoiety associated therewith.
 11. The electrode of claim 10, wherein saidat least one metal species having an organic moiety associated therewithis an organic salt of said metal, comprising a metal ion and an organicanion.
 12. The electrode of claim 11, wherein said metal is silver andsaid organic salt of said metal is silver benzoate.
 13. The electrode ofclaim 1, further comprising an ion-permeable material absorbed to saidsurface.
 14. The electrode of claim 1, usable for determining a presenceand/or level of a peroxide-containing compound in a sample.
 15. Asensing system comprising a sensing electrode according to claim 1, thesensing electrode being connectable to a power source.
 16. The sensingsystem of claim 15, wherein said sensing electrode forms a part of anelectrochemical cell.
 17. The system of claim 16, wherein saidelectrochemical cell further comprises an electrolyte, and wherein atleast a portion of said sensing electrode contacts said electrolyte. 18.The system of claim 17, wherein said electrolyte features an alkalinepH.
 19. The system of claim 15, being devoid of means for deaerating theelectrochemical cell prior to contacting the system with a sample. 20.The system of claim 15, further comprising a device for measuring anelectrochemical parameter of said sensing electrode.
 21. The system ofclaim 15, being configured such that upon application of a potential, aportion of said metal species is in a form of metal particles, saidportion being no more than 70 mol % of the total amount of said metalspecies.
 22. The system of claim 15, wherein said functional moietycomprises metal ions and wherein upon application of a potential, aportion of said metal ions is converted into said metal particles, saidportion being no more than 50 mol % of the amount of said metal ions.23. The system of claim 15, being configured such that upon contacting asample containing a peroxide-containing compound with said sensingelectrode, a presence and/or level of an electrochemical parametergenerated in response to applying potential to said sensing electrode isindicative of a presence and/or level of the peroxide-containingcompound.
 24. A method of detecting a peroxide-containing compound in asample, the method comprising: contacting the sample with a sensingelectrode according to claim 1; applying a potential to the sensingelectrode; and measuring an electrochemical parameter of said sensingelectrode, wherein a presence and/or level of said parameter isindicative of a presence and/or level of the peroxide-containingcompound in the sample.
 25. The method of claim 24, wherein saidelectrochemical parameter comprises an electrical current generated atsaid sensing electrode, wherein a presence and/or level of saidelectrical current is indicative of a presence and/or level of theperoxide-containing compound.
 26. The method of claim 24, being devoidof deaerating the system.
 27. The method of claim 24, wherein the samplecomprises oxygen.
 28. The method of claim 24, further comprising, priorto introducing said sample, repetitively applying said potential for atleast 5 consecutive times.
 29. The method of claim 28, whereinrepetitively applying said potential is performed such that a portion ofsaid metal species is converted to metal particles, said portion beingno more than 50 mol % of the total amount of said metal species.